Old One’s Army is something a lot of people don’t care to do. It is incredibly difficult, it’s like trying to reach wave 20 of the Frost Moon without lunar gear. Before 1.4.1, I never considered it worthwhile. However, almost of the weapons have recieved massive buffs and the role of Tavernkeep armors in hybrid builds is undeniable. After having taught myself to clear the event, I composed this guide to also help anyone else with enough time to waste on reading it.
Old One's Army
This guide is still a work in progress. I will update with any good advice from the comments and other potential strategies, as well as clean up the text once I have time.
GENERAL TIPS
Advice that applies to every wave of the event.
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Use the sentries. The number one piece of advice I can give you. In a class only run, it will be very difficult to make progress. The Old One’s Army sentries are so intertwined with the event for a reason, and should always be used regardless of class.
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The two sentries you should use are Ballista and Lightning Aura. Ballistas can be stacked near the crystal for the first few phases, and Lightning Auras can be stacked on the portals to neutralize weaker enemies. You can also use Exploding Trap, however it’s generally better to use your mana on the other two. I don’t recommend Flameburst.
-Between each tier of the event, grind out the current tier for the defender medals required for Ballista and Lightning Aura. This gives you a head start on each tier as you already have the good sentries you would otherwise have to grind the first several waves for over and over.
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Collect Etherian Mana and any heart drops between waves. This can help you heal quickly as well as prepare more sentries. Do note that enemies already on the battlefield remain after wave clear and should be killed before this step.
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Any gear you get from the Old One’s Army can help make the next couple of clears easier. Tavernkeep’s armors in particular propser during the event, allowing you to pair class damage and boost your sentries. Certain weapons from the bosses also work well for the event.
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Prioritize offense. Defense is cool, but the bulk of your build should go into offense. You have to keep your DPS up in order to not get overrun, and it’s especially important to do so against Ogre and Betsy.
-Try multiplayer. Despite health scaling, Old One’s Army is almost infinitely easier in multiplayer. Place one player on either portal and have them kill every enemy that appears. Give one player a Lightning Aura and the other a Ballista and have them use their own mana gains to build up sentry defenses. In tier 3, have one player hold off the ground mobs and the other bring Betsy into the sky. Makes the event manageable even if you slack on preparations.
TIER 1
Preparing for the event
This portion of the fight shuld be done post-Skeletron at the soonest. Outside of Master Mode, there is no gear from this event except decoration or vanity, so it can be done any time pre mech boss if you wish. Class loadouts are assuming a pre-Hardmode post-Skeletron build.
Flatten out an area for the event, perfectly level. You have a maximum space of 235 tiles to each side of the portal, however in prehardmode you do not have the mobility to deal with this full distance. I recommend around 125-150 tiles of room on each side of the crystal.
You should have campfires and life crystals readied for the event. Melee and Summoners should also place a Sharpening Station or Bewitching Table to either side of the crystal, close enough to be refreshed every wave.
Prepare the following buffs: Ironskin, Regen, Swiftness, Endurance, Wrath or Rage, Well Fed. Don’t use them right off the bat, they will run out. Use them starting Wave 3.
Recommended gear
All classes should have the following items:
-Ballista and Lightning Aura Rods. For the first run, start with Ballista and purchase Lightning Aura after your first clear.
-Shark Tooth Necklace. It would be redundant to list it in every class loadout. Pretty much a universal free damage buff, that gets better with higher attack speed.
Melee:
- Molten Armor
- Feral Claws. autoswing on Combat Wrench is invaluable.
- Combat Wrench. It’s a good, fast boomerang that can hit one target multiple times. Great for Dark Mage or wyverns.
- Sunfury. It is a good high damage piercing weapon for most enemies.
Ranged:
- Necro Armor
- Molten Fury w/ Jester Arrows. Their unlimited pierce should allow you to take out most peons and Dark Mage.
- Phoenix Blaster. It has no real CC benefits, only used for intruding Etherian Wyverns.
Magic:
- Jungle Armor or Meteor Armor. Jungle offers weaker damage but makes mana easier to manage.
- Magnet Flower and Celestial Cuffs
- Mana Regen and Magic Power potions
- Water Bolt. Pierces through 10 enemies and is slow enough with good enough knockback to damage multiple times.
- Demon Scythe is a high damage, 5-enemy pierce weapon that you should use on Dark Mage.
- Flamelash. Like Phoenix Blaster, use it to kill Wyverns.
Summon:
- Obsidian Armor
- Pygmy Necklace, Feral Claws. Feral Claws may seem like a strange choice, but autoswing on whips is massive.
- Summoner Potion
- Spinal Tap. Your strengh in this build is in the whip, take advantage of it. The whip can dispatch most enemies on its own.
- Vampire Frogs. They can deal decent damage to enemies on the ground by jumping through them and have high sustained damage versus Dark Mage.
- Imp Staff. Should not be your primary minion, but is instead used in tandem with Vampire Frogs. Vampire Frogs are best in small groups because otherwise iframes are used up, and Imp’s pierce can let it fill the gap. Use 3 frogs, and every other minion slot imps.
General strategy
Start by building up Ballistas. Once you have 2-3 ballistas on each side of the crystal, start placing Lightning Auras. The first run, you only have one of these until you can get 5 more medals. I recommend you start with Ballista.
Keep near the crystal. You don’t have the mobility during prehardmode to run around, so stay where you can see the crystal and watch for problems.
Wyverns are especially a problem in this phase. They distract your Ballistas, the one thing keeping you alive, and you aren’t strong enough to kill them before they come diving at the crystal. You may have to divert from your crowd control weapons and use pure DPS to kill them - Combat Wrench, Phoenix Blaster and Flamelash exist in the class loadouts for this reason. They will inevitably land shots on the crystal, but if you stand your ground you should be able to minimize their effect.
When Wyverns do start spawning, you’ll know ahead of time because your ballistas start to tilt upward to target them. Kill them as soon as you can, and then push back any approaching enemies that made distance while your Ballistas were distracted.
Right before wave 5, save your mana. Wait to see where the Dark Mage comes from, spawn all your sentries on the **opposite** side, and start wailing away at Dark Mage using your piercing weapons. This allows you to focus on the boss and keep the opposite side at bay at the same time. Watch for the dark mana ball which can hit for as much as 200 damage in Master, but aside from that you should be able to attack the boss freely.
Do keep an eye out for Wyverns as you kill Dark Mage. Your focus should generally be on Dark Mage and it won’t be realistic to keep every Wyvern off the crystal while still keeping your DPS up, but you do also want to make sure they don’t stack up too heavily because then they start to kill the crystal too quickly.
TIER 2
Preparing for the event
This portion of the event should be done after the mechanical bosses, and pre-Plantera. This allows you to have enough to take on the event while still letting the drops see utility.
Before killing the first Mech, grind 50 defender medals for Ballista and Lightning Aura Cane to give yourself a head start for the event.
Maximize the space you have during this event, since you now have the means to move around. Line the ground with asphalt. Like with Tier 1, prepare buff furnitures as well.
Prepare the following buffs: Ironskin, Regen, Lifeforce, Endurance, Wrath or Rage, Well Fed. Don’t use them right off the bat, they will run out. Use them starting wave 4.
Recommended gear
All classes should have the following items:
-Ballista and Lightning Aura Cane. Grind for these before killing your first mechanical boss.
-Queen Spider Staff is easy to obtain and is free damage, since it will not use Etherian Mana.
-Gelatinous Pillion in case you get hit by Ogre’s slime. It can also be substituted for wings altogether to make room for more offense.
-Clinger Staff and Nimbus Rod. Clinger Staff effectively keeps an entire half of the battlefield ag bay. You can place both nimbus clouds on the sides of the clinger fire to reinforce it even further, or placed opposite in order to weaken enemies from both portals.
Melee:
- Adamantite, Titanium, or Hallowed Armor. All three are generally similar in stats and offer different benefits.
- Squire Armor. You will have to grind the Defender Medals for it before killing a mech boss, however it’s generally very good due to the buffs to both melee and sentries. It can also be used in hybrid builds.
- Avenger Emblem, Fire Gauntlet
- Flask of Ichor
- Drippler Crippler. It does much the same thing as Sunfury in tier 1. It’s also a great choice for Ogre because it can throw piercing projectiles with decent damage from a safe distance.
- True Excalibur. Has range uncontested per its stage of the game, and pierces once, allowing it to take care of the immediate frontline. Don’t rely on it exclusively, because although its damage is good, it only pierces once and won’t keep up with approaching crowds.
- Bladetongue. Dangerous, but pays off with long piercing spray that spreads ichor. Not recommended for Ogre.
- Death Sickle. A good high-DPS weapon to kill clusters of approaching enemies. Not recommended for Ogre.
- Chlorophyte Saber. Does much the same thing as Death Sickle, except that Saber is easier to obtain and does it slightly less well. The difference is usually negligible and it won’t make a huge difference to just use Saber instead.
- Shadowflame Knife. A quick weapon to switch to to take care of immediate problems.
Ranged:
- Frost or Hallowed Armor
- Huntress’s Armor. If you grind the medals for it before the mech bosses, it allows you to buff both your ranged weapons and sentries to a reasonable extent, and can be used in hybrid sets.
- Ranger Emblem, Avenger Emblem
- Archery Potion
- Hallowed Repeater w/ Jester Arrows. Offers infinite pierce to take care of approaching enemies.
- Dart Pistol/Rifle w/ Cursed or Crystal Darts. Effective at quickly damaging the frontline, and does respectfully well for Ogre.
- Megashark w/ Exploding or High Velocity Bullets. Has great DPS for Ogre while damaging his immediate surroundings, and can quickly kill tankier enemies such as Drakins.
High Velocity Bullets have slightly more damage and more consistent, predictable pierce while Exploding Bullets don’t lose damage between multiple targets and have more knockback.
- Daedalus Stormbow w/ Holy Arrows. Blanket coverage over a large group of enemies, with inconsistent but heavy damage output.
Magic:
- Forbidden Armor. Not only will it buff both your weapons and your sentries, but it also offers the tornado to blockade enemies.
- Avenger Emblem, Celestial Emblem
- Mana Regen and Magic Power potions
- Life Drain. Good damage to clusters of enemies. Good DPS to groups of stronger enemies, but its area coverage is a bit worse.
- Magical Harp. The only mage weapon with unlimited pierce at its tier. Be sure to aim your cursor farther away from yourself to fire the musical notes f
- Cursed Flames. Blankets the area with bouncing and piercing fireballs with good damage and free DoT. You should try to bounce them very low so they can bounce through more targets.
- Golden Shower. DPS against even multiple targets is unimpressive compared to your other options, but it does spread ichor to five enemies at once and is a great secondary.
- Unholy Trident has a great combination of high DPS and some pierce, allowing it to cut down the immediate frontline including Ogre.
- Venom Staff. A large shotgun burst that can heavily damage Ogre if aimed from a 45 degree angle above him, and can spread into enemies even remotely near him. Not recommended before wave 7 due to its unreliable spread.
- Rainbow Rod packs good immediate DPS for Ogre while damaging nearby enemies, and can knock flying enemies out of the air.
Summon:
- Forbidden Armor. It is more effective than Hallowed for the majority of the fight, as your focus is not in the minions and the tornado is excellent at keeping enemies back.
- Obsidian Armor can be used during wave 7 to quickly kill Ogre using Firecracker.
- Flask of Ichor and Summoning Potion
- Pygmy Necklace, Summoner Emblem, Berserker Glove. Berserker Glove offers autoswing on whips.
- Durendal. Generally good for the event being a whip, and will be your main damage for much of the event.
- Firecracker. Its immediate damage, attack speed and linear piercing are all inferior to that of Durendal, but it’s better than Durendal for Ogre when combined with Obsidian Armor thanks to the unique tag bonus.
- Sanguine Staff. Stupidly strong minions even if you don’t have many of them, and they can quickly kill enemies approaching from all angles.
- Blade Staff. DPS just underneath Sanguine when you stack ichor and whip tags, and it has an advantage in being able to slice through multiple enemies in a swing. You shouldn’t use Firecracker if you choose these over Sanguine.
Note the use of Avenger Emblem in all classes except Summoner. This is important because it buffs both your weapons *and* your sentries.
General strategy
Tier 1 is very easy in comparison to Tier 2 and 3. This is the point where you will probably start to struggle with the event.
First off, take advantage of Queen Spiders, they are strangely powerful for their tier and will tear down the frontline. They can be added with no etherian mana cost, so there’s no reason not to.
Definitely use a Clinger Staff. If you’re in a Crimson world, bring some corruption in using the dryad and take the time to farm for it. It’s basically an impenetrable wall with knockback that keeps an entire side of the arena at bay, which makes the event infinitely easier to manage. Be sure to recast it between waves.
Continue the trend of ballistas on the crystal and lightning aura on the portal. This time around you want a thicker wall of Ballistas before you start with the Lightning Aura, I’d switch focus after around wave 4 or 5.
At this point, you have the mobility to dart around and kill enemies as they appear, but still keep an eye on the crystal. Wyverns,and Gliders can snipe it when you aren’t paying attention. They aren’t nearly as disruptive as in tier 1 and can be killed quickly, but you want to avoid the chip damage.
Wave 7 is the hard part of the event. Ogre is fast, and will quickly reach the crystal. But unlike tier 1, you can’t afford to direct your full focus onto him either as the smaller enemies *will* surmount your defenses. Begin to wail on the Ogre as early as possible, but keep a good eye on the crystal.
You’ll have to alternate between Ogre and the enemies on the opposite side in order to hold off the defenses. Your focus should generally be on Ogre, but you should watch the opposite side and blow them back if they begin to make too much distance. I listed in the class setups a few decent weapons to help dispatch Ogre while still damaging his immediate surroundings.
Note that Ogre will only target the crystal when he is more than halfway to it - otherwise he will focus on you. You can use this to your advantage to slow him down, but eventually you will have to stop in order to attack the opposite side of the arena.
DO NOT APPROACH OGRE. Attack him from a safe distance, or he will devastate you with his swipe and slam attacks. Also watch the slimeball - while its damage to you and the crystal is negligible, it’ll ruin your movement speed. I recommend all builds to bring a Gelatinous Pillion just in case of this scenario.
TIER 3
Preparing for the event
This portion of the event should be done as late as possible before the Lunar Events. It is quite difficult, and its loot is most effective for Pillars and Moon Lord.
Before killing Golem, grind 200 defender medals for Ballista and Lightning Aura Cane to give yourself a head start for the event.
Use the full space allowed and an asphalt floor from tier 2. In addition, build several rows of platforms above the Crystal, about 30 tiles up and 20 tiles apart. Stay on the ground for most of the event, this arena is specifically for Betsy. Be sure to keep using buff furniture.
Prepare the following buffs: Ironskin, Regen, Lifeforce, Endurance, Wrath or Rage, Well Fed. Don’t use them right off the bat, they will run out. Use them starting wave 5.
Recommended gear
All classes should have the following items:
-Ballista and Lightning Aura Staves. Grind for these before killing Golem.
-High tier wings, a form of dash, and Soaring Insignia. Although mobility isn’t usually a prime focus for Old One’s Army, the mobility is essential for Betsy. You can switch them on just before the boss spawns.
-Clinger Staff. Its damage doesn’t do nearly as much in this tier, but it still does exactly what you brought it in for - blocking off smaller enemies from an entire half
Melee:
- Beetle Armor, with Scale Mail. Best melee offensive build available.
- Valhalla Knight Armor. Requires you to grind out the Defender Medals before killing Golem. Slightly less profitable for melee itself, but buffs your sentries significantly and provides regen. Also used in some very good hybrid sets for all classes.
- Destroyer Emblem, Celestial Shell, Fire Gauntlet
- Flask of Ichor
- Terra Blade. Being buffed in 1.4.1, it should really be plenty enough for this event. Its crowd capabilities are massive as the sword beam can cut through the frontline and push everything back, and you can usually rush down with the blade. Better than Influx Waiver for this event.
- Seedler. Better than you’d expect as it blankets the ground with shrapnel. Great at damaging or killing enemies approaching from both directions at the same time.
- Starlight is able to decimate stronger enemies at close range.
- Flairon is particularly good versus Betsy, as with other fast flying bosses.
Ranged:
- Shroomite Armor. USE YOUR STEALTH. This is pretty much the only point in the game where you can afford to attack while standing still, and it will let you completely devastate everything up until Betsy.
- Red Riding Armor. Requires you to grind Defender Medals before killing Golem. Boosts are almost equal to those of Shroomite, with sentry bonuses thrown in instead of stealth. Almost certainly better than Shroomite during the Betsy fight since you won’t be using your stealth. Can also be used in hybrid builds.
- Destroyer Emblem, Celestial Shell, Sniper Scope
- Archery Potion
- Eventide w/ Woodern Arrows. Eventide is simply all you need up until Betsy. It has pierce strong enough to cut down everything, and excels in damage output.
- Stake Launcher. Lesser damage than Eventide and loses damage as it hits targets, but it does the job almost as well and can be substituted with little loss if you want to do the event earlier.
- Tsunami with Holy Arrows. Should be your choice for Betsy, as it is a great boss killing pair and will excel in single target.
- Xenopopper w/ High Velocity or Chlorophyte Bullets. Its single target DPS is good and it can damage the immediate frontline to a certain extent. Against Betsy, it can be paired with Chlorophyte to aim more reliably. Generally outclassed by the bows but can be used as a gun user.
- Snowman Cannon. Unlike most weapons in the event, it does best if aimed from above. Higher tier nukes give it a wide explosion area that smashes a large number of enemies at once. Also the best rocket for Betsy, although the snowmen can be distracted.
- Electrosphere Launcher. Good at stunlocking the immediate frontline for a good period of time, allowing you to slow down crowds significantly by switching between it and another weapon.
Mage:
- Spectre Armor w/ Mask. Don’t use the hood, its lifesteal is good for literally anything else but you cannot afford to lose so much damage.
- Dark Artist Armor. Requires you to grind out the Defender Medals before killing Golem. Has very strong boosts for both Mage and your sentries, and has a particularly notable hybrid set: Hallowed Headgear, Spectre Chestplate, Dark Artist’s Leggings.
- Celestial Emblem, Celestial Shell, Destroyer Emblem
- Magic Power and Mana Regen potions
- Charged Blaster Cannon. Can basically win the event by itself, killing the entire line of enemies in one blast and delivers uncontested damage to Betsy. You shouldn’t need anything else, but I will list other options in case you can’t obtain it.
- Razorblade Typhoon. Despite being nerfed for crowds, is still one of the best weapons for this event without going into the lunar events.
- Nightglow. Better single target DPS for Betsy than the Razorblade Typhoon, at the cost of inferior crowd capabilities.
- Magnet Sphere. Free DPS and glides over crowds of enemies for steady damage. Make sure not to switch to it if you desperately need piercing.
- Rainbow Gun. Can be propped on one portal to kill any weaker enemies. During wave 7, it fan also be lined up with the ground near the crystal to support your defenses.
- Clinger Staff and Nimbus Rod. Do the exact same thing I described in Tier 2, and still do that well despite being pre-mech weapons in a post-golem stage.
Summon:
- Spooky Armor
- Valhalla Chestplate, can trade out 2 minions for some life regen. It exists as an option, but for this event I recommend going for the offense on Spooky Armor.
- Papyrus Scarab, Hercules Beetle, Berserker Gauntlet
- Flask of Ichor and Summoning Potion
- Terraprisma (if you can). It is immensely powerful and will instantly neutralize anything that comes close, and will kill Betsy before anything can go wrong. The equivalent of a Moon Lord drop available pre-Pillars.
- Xeno Staff. It will do only alright for Betsy, as she is fast enough to keep them from attacking quickly, but it is still the one of the best choices behind Terraprisma. Ravens can be shaken off and Sanguine will not win the urgent DPS race.
- Desert Tiger. Surprisingly effective versus Betsy following its 1.4.1.2 buff. You’ll have to lead Betsy a bit farther from the crystal while using it because peons will distract it more easily than other minions, but it pulls great DPS. Synergizes with Firecracker.
- Dark Harvest. Distributes damage from minions into the crowd, but also tears down clusters already with its fast speed. Use for waves 1-6.
- Kaleidoscope. It is the absolute best whip for bosses and should be used versus Betsy.
- Firecracker (ONLY with desert tiger). Better than Kaleidoscope for this particular minion because the explosions almost triple its already insane base damage.
General strategy
You can use side sentries for tier 3, but they won’t be as effective. Queen Spider’s DPS is less impressive in the post-Golem stage and Frost Hydra has very limited pierce.
Definitely still use Clinger Staff, however. Its knockback will hold back an entire side of the battlefield and make it impossible for smaller cannon fodder to get through.
Continue the trend of lightning auras on the portals and ballistas on the crystal. Tier 3 lightning aura is actually kind of stupid, so I recommend placing one on each portal
before stacking Ballistas and then switching back to Ballistas until around wave 5.
Don’t fool yourself thinking wave 2 is free enough to just run back and forth and spam kill. The Lightning Bugs will approach the crystal relatively quickly and will deal a ton of damage to it while you aren’t watching. Stay put next to the crystal and kill the lightning bugs as they approach.
Be cautious of Ogre in waves 5-6. He won’t be the same impending death sentence that he is in tier 2, but he can get himself near the crystal before dying. Prioritize him for DPS, but as in tier 2 be cautious of flying enemies or the ground enemies on the opposite side. Dark Mage can probably be almost completely ignored.
It is *essential* to clear wave 6 with enough time to spare. You want time to finish setting up your wall of sentries and want to make sure there are no strong enemies left
before Betsy comes barreling in.
Think of wave 7 as a DPS race against Betsy. Your damage focus should be completely on Betsy and you should allow your sentries to take care of the ground enemies for as long as possible. It is important to have enough sentry defense to ward them off while facing Betsy.
Betsy is also the reason I suggested platforms above the floor of the event. Fighting Betsy on the ground is a good way to get cornered into the peons, so having an arena specifically for Betsy just above the battlefield will be immensely helpful.
Betsy is generally a fight like Duke Fishron. You want to be moving quickly and constantly, which is difficult during an event such as Old One’s Army, but important. I strongly recommend good wings, a dash, and Soaring Insignia - a UFO mount just won’t give you the mobility you need.
Her dash and spin attacks can be avoided with good movement speed and some weaving, just like Duke Fishron. Generally keep your distance from Betsy as to not get cornered by these attacks. Betsy also has two downward attacks that force you to try to stay above her. The firebombs that she drops can harm the crystal, but they can also be destroyed by the player. Her firebreath can be avoided by either weaving straight up or down, but you need to react quickly.
Etherian Wyverns will be the death of you during wave 7. Because so many flood in from the Portals and Betsy herself spawns more, it’s not realistic to kill them all. They will get up in the crystal, which is why it is so important to kill Betsy as quickly as possible to end the event. I do recommend quickly killing any Wyverns that you do happen to see just to give yourself more time.
Don’t expect to clear this wave your first try. Betsy is difficult, and you will have to learn her patterns the same way you had to learn Duke Fishron or Empress. Be prepared to do this event over and over again until you can manage Betsy well enough to kill her.
ALT STRATEGIES
Ideas that you can try for the event if you need more help. These can help you with certain problems but also pose their own issues.
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Boulder statues
Boulder statues hooked up to a timer will kill most smaller enemies in tier 1 of the event. Before starting the event, test them to make sure they do not roll into the crystal. After wave 1, the risk boulders pose to you will not be worth the damage they can deal to enemies.
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Ballista tower
Placing a small cieling above the crystal and placing Ballistas on top to snipe flying enemies. It may block your other attacks and doesn’t stop wyverns from interrputing ground sentries, so it may not be worth the mana. Try it and see if it helps you.
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Crystal shield
Actuators can still be used during the event and inactive blocks aren’t counted when starting the event. You can use this to create a box around the crystal. It won’t protect against enemies which can all phase through tiles, but can block Drakin or Betsy projectiles. Note that this is a double edged sword as it makes it harder to fight off Wyverns and you’re screwed if enemies get inside the box.
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Traps
Also using actuators, Lihzahrd traps can be used to deal limited damage to all enemies in the event. Enemies in OOA only take half damage from traps and they post a significant threat to you, however.
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Delaying progress
The majority of this guide is assuming you want to use the drops, but if you’re only going for achievements, you can probably delay the event as long as possible. Pre-mech Hardmode weapons, post-Plantera weapons and Moon Lord drops will all mindlessly kill their tier of the event even without sentries.
-Crystal luring
Betsy treats the crystal like another player. Use this to your advantage, grabbing items that reduce aggro and keep Betsy distracted while wailing away. This only really works with Shroomite stealth, almost nothing else can kill Betsy before she kills the crystal.
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It’s not an exaggeration to say the Old One’s Army is the hardest fight in the game. Were it not, I would not have written this guide. If anyone has anything to add, please say so, I’d love to make this guide as effective as possible.
