Oh boy, this is a mess. You absolutely shouldn't add any more to this unless you fix what's already here.
-The world has a greater chance of having the worst of two ores that can be chosen, including the Hardmode ones. That is, more chance to generate with Tin than Copper, Iron than Lead, Silver than Tungsten, Gold than Platinum, Cobalt than Palladium, Mythril than Orichalcum and Adamantite than Titanium;
"Oh no, I have like 2 points less of damage"
Except in hardmode where I can just fish for the better ores anyway.
-Increased chance of the evil biome having more area at the beginning. That means that the Crimson or the Corruption will probably start in the game with more area than the normal size;
Does that mean more chasms?
-The player will start without its axe. That is: NO AXE, because who needs to start the game cutting down all the trees? Now, to make this mode harder, you will need to start mining to make your first axe, that will probably be made of Tin;
Ok lol, I'll just use bombs to get wood then.
-Your Shortsword and Pickaxe are made of Tin, because that's the worst counterpart possible, and, to make it harder, both your Pickaxe and Shortsword will have the Broken modifier;
...you realize that tin is stronger than copper?
-Lava hurts 50% more at the Underworld;
Should have been a change expert made to be honest.
-From 11AM to 01PM, at the Desert, the player gets the OnFire! DeBuff;
A.K.A just wait 30 seconds if you want to pass through this biome. This adds no difficulty, just tedium.
-OnFire! Debuff and other fire DeBuffs take more time to stop at hot places like the Desert and the Underworld;
That's almost completely meaningless and does borderline nothing to hinder the player unless they already took damage.
-Player gets Chilled DeBuff if he/she is at the snow and it's raining (Snowstorm/Blizzard);
Interesting way of giving the snow biome it's own version of a sandstorm.
-If the player is wet (or just got out of the water) and he/she is at the snow biome and it's raining/storming, he/she gets stuck in ice (Frozen DeBuff);
A.K.A. Kill the player literally over a minute later for touching liquid. Also they can't move because that's fun. You may as well just make water an instant death trap at that point.
Also, you could end up softlocking someone if they had a Neptune's Shell, that's not cool.
-Every time it rains there is a Sandstorm at the Desert;
Shouldn't this be tied to every time there's a windy day?
-Sandstorms have a 30 to 40% chance of occurring without it raining, per day;
"let's just make the desert impassable so they just bridge over it instead of ever bothering to explore it"
-Zombies are capable of opening doors without need of a Blood Moon;
-Players don't care because they can still just put a torch behind the door and stop them anyways.
-Demon Eyes pass trough Blocks like servants of Cthulhu already do;
What does this even add to the difficulty? Do you
want people to just not ever be on the surface in earlygame?
-All enemies that inflict the Poisoned DeBuff will now inflict Venom DeBuff instead, including the Queen Bee;
You may as well just make them deal more damage at that point lol.
-Greater chance of a Guide Voodoo Demon Spawning instead of a regular Demon at the Underworld;
Quality of life change which makes the game easier, actually.
-All enemies and Bosses think faster. That is, they attack faster;
Define "attack faster". Do you mean less downtime between attacks or less duration for all of them? Because if you just blanket everything with
either then it'll actually make some attacks easier to deal with.
-Increased chances of getting the Gold portal from breaking a pot;
I actually like this.
-Explosives like bombs (dropped from Clowns and Skeletron Prime) now break Blocks;
How does this make
literally anything more difficult? You're not making them more difficult to dodge in any way or even altering their stats, you're just adding tedium.
-All Death Rays (Martian Saucer and Moon Lord ones) pass trough Blocks;
This is already a thing as of 1.4.
-1/3 chance of a slime rain occur per day;
Okay lol. I'll just be hiding underground because of all the random bull
you've been throwing at me for existing on the surface anyway.
-Blood Moons have increased chance to happen;
Okay lol. I'll just be hiding underground because of all the random bull
you've been throwing at me for existing on the surface anyway.
-New Exclusive drops from all Bosses;
-All Bosses now have a second phase, that is much more violent and agressive, and those Bosses who already had a second phase will keep how they were;
You gotta be more specific with these.
-The player will get two drops of the drop list from a Boss;
Expert Mode has always done this.
-Eye of Cthulhu has 50% chance of spawning every night before being defeated;
Okay lol. I'll just be hiding underground because of all the random bull
you've been throwing at me for existing on the surface anyway.
-Skeletron's Head is invincible before the player kills his hands;
Pretty much what Expert already does.
-Bee hives now have two Larvae instead of one, that can each summon one Queen Bee, so there are two Queen Bees;
...or you could just be careful and break them one at a time. Thanks for the extra boss summon lol.
-At the Hallow biome there's a chance of Queen Slime spawning naturally;
Okay lol. I'll just be hiding underground because of all the random bull
you've been throwing at me for existing on the surface anyway.
-Skeletron Prime's head will be invincible until the player kills his four arms;
This does absolutely nothing to make this fight more difficult and just extends what's already an incredibly long winded and drawn out "boss fight" with a glorified punching bag to begin with. Tedium is not difficulty.
-The player will need to kill every body part of the Destroyer (and its Probes) to make the Boss count as defeated. That is, the player needs to hit each and every segment of the Boss, and then kill the Probes. When the last probe dies, the entire Boss breaks/dies and it will drop the drops;
Tedium is not difficulty.
-The three Mechanical Bosses can spawn at the same time naturally, plus, each one has 10% chance of spawning at the first night after defeating the Wall of Flesh;
Okay lol. I'll just be hiding underground because of all the random bull
you've been throwing at me for existing on the surface anyway.
-If all three Mechanical bosses have been defeated, there's a 0,5% chance every day that Duke Fishron will spawn naturally at the beach;
Okay lol. I'll just be hiding underground because of all the random bull
you've been throwing at me for existing on the surface anyway.
-If all the Mechanical Bosses have been defeated, there's a 5% chance that Plantera will spawn naturally (only at the Jungle);
Another problem with summoning bosses randomly?
I literally could just use my magic mirror and despawn it for free.
-If Plantera has been defeated, Duke Fishron's chances of spawning (if he was not defeated already) increase from 0,5% to 10%;
Okay lol. I'll just be hiding underground because of all the random bull
you've been throwing at me for existing on the surface anyway.
-If Plantera has been defeated, the Empress of Light has a 5% chance of spawning naturally at the Hallow;
Okay lol. I'll just be hiding underground because of all the random bull
you've been throwing at me for existing on the surface anyway.
-Golem's head now needs to be defeated too to count as the entire Boss defeated, but it still can't be killed nor damaged before all the other body parts;
Tedium is not difficulty.
-All the four Lunar Pillars' shields will need from 2 to 3 times more enemies killed to be released;
Tedium is not difficulty.
-After the player releases a Lunar Pillar's shield, the Pillar will switch places with another Pillar (by teleportation)
and if the player goes at it, it will try to defend itself;
For the first part: Tedium is not difficulty.
For the second: be more specific with how it defends itself. Does it get new attacks or use the same ones from the event which are basically useless?
-If the player released a Pillar's shield, but takes too long to kill it, the shield will regenerate and come again with the same health stats;
Tedium is not difficulty.
-After all the Lunar Pillars were killed, Moon Lord will only take 30 seconds to spawn;
This is actually a pretty nice quality of life change which means you don't have to wait so long every time.
-Moon Lord will keep more time with his eyes closed;
A) This means he's going to be attacking less and therefore be much easier than normal b) ...Tedium is not difficulty
Again, don't add any more. First, reevaluate what you already have and either make it better or remove some of it.