Terraria Community Forums

Lunatic Cultist, as he's fun to fight, and one of the most challenging characters to fight. He also looks very cool in my opinion.

Lunatic Cultist is definitely a favorite of mine, but my favorite would likely be Skeletron Prime. He isn't THAT challenging if you're prepared, but the fight's just really chaotic and fun. I'm also quite a fan of his design as well.