As the title states, this is how to kill Skeletron Prime easily. First, you should have melee adamantite armor. You can use any accessories you want but I recommend angel or demon wings, a cross necklace, a cloud in a bottle, a philosopher's stone, and an obsidian shield with all accessories reforged to warding. Next, you want a megashark with about 3000 crystal bullets. (The megashark can be any reforge but unreal is the best.) Then you want to make a long wooden platform arena that is also about 10 to 30 stories high. Then you want to summon him and try to kill his hands first and then his head is easy. (You might also want to make a bed to set your spawn so if you die he won't go away.) And that's how to easily solo Skeletron Prime!