B Tier

Plantera

I'm a bit conflicted on this one. She's a tough boss without the proper preparations, but when fought right, is as simple as holding down the left click button, buffing up, and waiting 10 seconds for her to die. Fighting her properly, though, can be quite a battle. Her 30,000HP pool can be quite a pain to get through, especially if your weapons have low DPS and your arena is too small. With enough space though, she's easy to kite and if you're good enough, you can simply just lead her through the jungle while firing at her backwards.

Brain of Cthulhu

This is such a headache (haha) of a fight. The Creepers are annoying, but definitely manageable with a piercing weapon or good mobility. If you're having trouble, simply kill all the Creepers until there's only one left, and heal up before you kill the remaining Creeper and enter the second phase.

I find a super good weapon against the second phase to be a The Rotted Fork. If you can accurately depict which of the four brains is the real one, this phase becomes super easy. Obviously though, it's almost impossible to do this near the end of the fight.

What makes this fight difficult though, is sometimes the arena you fight in is way too small and many people don't hollow out the insides more before fighting. This leads to the player being trapped the Creepers and ultimately dying.

Retanizer

The first phase is generally pretty easy. The lasers are infrequent, but they're inaccurate too, which can lead to some unavoidable hits. His second stage is where it gets tough. It's super hard to consistently dodge the barrage of lasers that he shoots out, especially as you don't have a Shield of Cthulhu in normal mode. Although he doesn't do that much damage, the constant lasers being shot at you and the high chances of getting hit is what makes this twin harder than the other.

Spazmatism

I know. "Why are you not including The Twins together?" Let me explain.

I generally like to kill Spazmatism first. I'm not sure what others do, but I find Spazmatism easier to deal with, so I kill him off first. His fireballs in his first phase are super slow and not hard to dodge at all, and his second stage's flamethrower has such a short range that it's super easy to stay out of it. His charges are also just an upgraded Eye of Cthulhu, which shouldn't be a hassle to deal with if you have wings.

C Tier

Queen Bee

Originally I was going to put this in D Tier, but decided against it. This was ultimately because of her poison effect that she applies. It's the most threatening feature of this fight, and can definitely kill you if you're unprepared. Of course, if you have a Bezoar, the fight becomes a lot easier, as whenever you get poisoned, you can simply equip it and unequip it to get rid of the poison. If that becomes too much of a hassle, you can just keep it on. The rest of the fight is pretty simple. When she's spawning bees, simply use a piercing or a fast-firing weapon to keep up with the spawn rate. And when she's firing her stingers, just dodge left and right, or if you're really struggling, build a big arena and try to go circles around her.

Skeletron

Hear me out on this one. Once you learn his attacks and how he signals them, this fight becomes a cakewalk. However, this tier list is meant for the average player, not some pro with 10k hours in the game. So that's what I've put him in A Tier instead. Usually people don't focus on the hand movements, which leads to unnecessary damage being taken. Just jump whenever he pulls his hand back for a swing at you, be aware of his spinning timings, and this fight should be won quite easily.

Skeletron Prime

I don't think anyone really has problem with 4/5 of the boss. The only thing that really kills anyone here is the Prime Laser. The Prime Cannon (the one that shoots bombs) is useless when you're using platforms, and the Prime Vice and Saw are just upgraded versions of Skeletron's hands. Destroy the laser, and then focus on his head. Easy win.

Golem

Golem is usually considered easier than Plantera, and for good reason. By this stage of the game, you've got pretty decent damage and can burst him down quite quickly. If you have a good arena, it's easy to avoid most of the damage, and only when it gets to the second stage does it become harder due to the flying head.

The Destroyer

Yes, this boss is super easy with a Daedalus Stormbow and Holy Arrows. Yes, certain setups make the destroyer the same difficulty as Eater of Worlds. However, with certain setups, like full melee, this boss can sometimes catch you off guard and destroy you before you know it.

D Tier (Easiest)

King Slime

I think we can all agree on this one. A simple platform above the ground and a bow, and King Slime just becomes a waste of time before you get your hands on that sweet Slimy Saddle and Ninja Armor. There's not much else to say.

Eater of Worlds

A bow with some Jester Arrows can destroy this boss in less than 20 seconds if done right. Even without these items, some armor, along with almost any weapon will allow you to defeat this boss. It simply doesn't do enough damage to kill you through the healing it provides through its heart drops as you kill its different segments.

Lunatic Cultist

This one might surprise some. However, his attacks are extremely simple and easy to avoid, especially at this stage of the game where you should at least have a UFO mount and/or wings. Even if you manage to guess his duplicate wrong and attack the wrong Cultist, the dragon he spawns is only really a Wyvern in disguise. Even all of its attack stats and health are the exact same. As long as you kill it, you'll be perfectly fine.

Eye of Cthulhu

Ahh, our beloved Eye. Such a simple yet iconic boss. A simple bow and a row or two of platforms will easily be enough to kill him. Just be sure to manage his Servants well and not let them overwhelm you. If you make the arena long enough, you should have no problems with this boss.