PixelPete
Skeletron
Fetid baghnakhs work best for that (probably butchered the spelling)On this thread, you can post any little tips, tricks, or advice for playing Terraria.
My tip is that when you are first fighting the Eater of Worlds get a sword that does a decent amount of damage and autoswings. Then, just stand right where the EoW comes at you and smack its head with the sword. If successful, you should kill off its body parts in one big streak.
Share your tips down below!