Skeletron Prime is the Hardmode version of Skeletron.It is made out of metal just like The Twins and The Destroyer.The parts of Skeletron Prime are the Prime Vice,the Prime Cannon,the Prime Laser and Skeletron Prime's head.He can be summoned by using the mechanical skull at nightime in any biome.Like Skeletron,he starts spinning his head and his defence drops to 0.But this time spikes come out of his head to do more damage.