Alright, I play on expert mode, so I'll sort them accordingly...
1: King Slime (the rope trick makes it actually impossible for you to get hit by him unless a demon eye decides to do a funny joke)
2: Skeletron Prime (his melee arms are really easy to dodge and you can just dodge his projectiles by literally flying in one direction with wings)
3: Golem (This boss is easy even if he isn't trapped, I don't get why people even bother...)
4: Brain of Cthulhu (Creepers die too fast and illusions are easy to see through)
5: Eater of Worlds (he simply doesn't do enough damage and doesn't have enough health...)
6: Wall of Flesh (He would be hard... If bee weapons didn't exist.)
7: The Destroyer (He would be hard... If the Daedalus Stormbow didn't exist.)
8: Lunatic Cultist (I've fought him so many times that I rarely get hit... my stupid minions keep summoning Phantasm Dragons though. He probably deserves to be lower on this list but I need to give credit to my favorite boss.)
9: The Twins (eh... I don't really know... I just have a bit of trouble with these two for one reason.)
10: Skeletron (his arms are easy to dodge because of how telegraphed they are. The skull projectiles, however...)
11: Queen Bee (I don't know why I hate this boss so much... THANK RED FOR THE SHIELD OF CTHULHU!)
12: Duke Fishron (I find his dashing easy to dodge with an antigrav hook and a spammy weapon... Phase 3 is still hard though.)
13: Plantera (I have a very quick but risky strategy, getting in close and flying in tight circles over and over during the first phase and running like heck during the second phase! I usually die in the first phase though... but at least the second phase is easy because there aren't projectiles.)
14: Moon Lord (This boss is harder then you think... it's not the phantasmal deathray that kills me, it's the coordinated attacks the true eyes use, the deathray is easy to dodge, why do people block it?)
15: Eye of Cthulhu (I'm being completely serious here... Why is he hard...? Because I normally fight him very early on... and then he has a new attack in his second phase in expert mode that is literally impossible to react to fast enough and requires a LOT of mobility to avoid. I absolutely HATE this boss and dread fighting him in hardcore expert...)
Edit: forgot to mention that I sorted them by the difficulty when you fight them as soon as possible, not with an endgame character
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Heck yeah. With the nurse (paired with Solar Eruption) it's ALMOST the easiest boss in the game. Slime King is slightly easier due to the rope strat.
I don't think that's a valid statement anymore, Cenx said she was patching that in 1.3.6