King Slime - Not a hard at all boss, considering he's affected by terrain and isn't immune to lava nor fire. Its only move is also jumping around, which is quite easily eluded.
Eater of Worlds - This boss only ever gives me trouble in Expert Mode, if anything. Its AI is literally the same as the worm enemy's. It's also quite slow, and its movement is predictable- it moves straight towards you and doesn't even try to form a full circle around you. This is a cakewalk, especially in the surface.
Brain of Cthulhu - Not that hard. Only fought it once, and it can be challenging to dodge at times, but it has relatively low health, so, fun, I guess. The creepers can be a nuisance against you with a weapon possessing a knockback of almost 0, but you'll most likely have a better weapon than that by the time you go fight it.
Queen Bee - Considering it only ever charges straight at you, and hovers above you sending bees, without it ever despawning depending on time, I feel like this boss is even easier than EoC. If you have rope or rocket boots or literally anything of the like, even a considerably good arena, its charge attacks are next to trivial. And the bees are only a pushover- they never affected my gameplay. If one does hit you, it sure can knock you around, though.
Eye of Cthulhu - It sends actually considerably notable servants after you, and chases you faster than EoW, and from any direction to any direction. Its servants drop hearts, at least. Its spawning requirements are quite low, but the first fight's timing is also RNG (and of course, luck)-based. Its second phase is more aggressive, but it doesn't spawn servants anymore.
The Destroyer - Yes, a mechanical hardmode boss is placed here. Why? Because I defeated it with a tool. Not really, but its probes are a huge disadvantage to it, seeing as they give health a lot of the time. Piercing weapons are almost unfair against this boss, because of how overpowered they are against it. It can also only go up to a certain height from ground blocks, so if you're above that limit, you can wish it good luck when it's desperately trying to hit you.
Skeletron - For some reason, I have a bit of trouble fighting this boss. It has only one spawning requirement, for it to be night (and for the old man to be present, but he's gonna be there). Its hands swing at you from both sides. However, when it has its hands eliminated, it's a really, really easy fight. So easy, in fact, that its only move is slowly spinning towards you. Very slowly. It can chase you at a considerable speed as well.
Wall of Flesh - This one mostly depends on the arena you've made, or not made. If it's a straight line, expect this to be a cakewalk. Its minions aren't very effective unless in Expert Mode. Its lasers can give trouble, but it mostly depends on the arena, again. In Expert Mode, its fastest speed is also really, really fast, but in normal mode, running boots will make its speed tolerable and possible to deal with in a fair manner.
Skeletron Prime - It's Skeletron again alright. I think the laser is the only limb I ever needed to get rid of, but I died to the cannon too, as its bombs weren't the most notable things in the dark. The vice and saw aren't very hard to deal with. The only worry you have is time, because if it runs out, it will kill you upon hitting you instantaneously. It's considerably quick to catch up to you too.
Plantera - This one very much depends on if you have a cobalt shield or not, and I did, so that's great. The first experience I had with Plantera was when its thorn balls dealt 120 damage, but that's no longer even nearly the case. Its seeds can be subtle or even camouflaged against the background of the jungle, but... well, nothing for the but. Anyway, while it's difficult, you just need a wide and open spot to fight it in, in order for a considerably successful battle (according to just me anyway).
The Twins - These are by far the most troublesome mechanical boss I came across, and while I think Spazmatism is tougher, Retinazer gave me quite a hard time as well. The problem with both isn't their first form at all, it's their second forms, and here's why- Spazmatism chases you and if it even gets near you, it shoots cursed flames which have a considerable damage and range. Retinazer was annoying with its lasers, but they were easy enough to dodge (just like the Wall of Flesh, a straight line as an arena should work).
Duke Fishron - Golly, this boss is definitely what I had the most deaths with. A straight line is an okay option, but Duke and his attacks are quite swift. You need to dodge and move around a lot, but the minimap is a great help when it comes to targeting. Most dying didn't really mean most challenging, as I tried the wrong strategy over and over again.
Golem - Its fireballs and lasers in such a small arena as the Jungle Temple is... at least its body was large, and wouldn't pass through solid blocks. Anyway, its hands were a cakewalk, but its second phase was no joke (for me, at least). The arena is the problem, and unless thanks to a generation error, you can't move the altar you use to summon the Golem.
Moon Lord - Now, the eyes give me trouble, but the so-called death beam doesn't even go through dirt blocks. Really? Anyway, most of its attacks are swift, and it can spam attacks, but if you have good enough wings or shoes, you'll just be running away from a wall of its attacks. It'll always keep up with you, you can't run away from it. It has multiple health bars assigned to body parts. And that's about it. Its targets' hitboxes aren't the biggest, but...
Lunatic Cultist - They're certainly bigger than Lunatic Cultist's. This boss is definitely what I had the most trouble with ever in the game, and its small body didn't help at all, and the fact it takes about a third less damage from homing projectiles didn't help at all! Its decays' summoned enemies are sometimes just another nuisance, its attacks are cleverly designed, it teleports ALL THE TIME, just what is with this maniac? Anyway, this is just an exaggeration- it does have its weaknesses too, such as its attacks being easy to avoid from a distance. Maybe I was just luckier with the Moon Lord, but the cultist was a tad harder overall, in my humble opinion.
I respect anyone's personal lists and opinions, and that concludes this, so cheers!
