Dumb Bosses

Jim Jimmothy is a pink humanoid that is a quite basic boss. 

Stack King is a grey humanoid with a crown that has an odd ranged attack that summons stone pillars.

Lorbths are fish monsters that dwell in swamps and mangrove swamps. They drop slime on death. Also they aren't bosses.

Malawar is an undead humanoid found in the soul sand valley. They fire projectiles that spawn wither skeletons when they hit something.

Switchblade is a humanoid covered in armor. He melee attacks, and touching him inflicts weakness.

Chopps is a flying humanoid with a pair of rotors. He uses melee attacks, and touching him pushes you away.

Also his name isn't actually chopps but the other bosses call him that.

Reeds is a green humanoid with a wooden mask and a mohawk. He can spawn in jungles and turn invisible. 

Splittzber is a purple humanoid with small spikes in its head. When damaged, it teleports away. On death, it also has a special little thing it does. Also it spawns in end highlands.

Gild Lord rules over the gildlands. Runs at people with two golden rods. Must be summoned.