The Mechanical Skull is a boss-summoning item used to summon Skeletron Prime, a Hardmode version of Skeletron. It can only be used at night, which means consuming this item during day will not spawn Skeleton Prime. It is also unusable when the boss is already present. It can be used in any world, but usually only becomes accessible in a Hardmode World. If Skeletron Prime has not been defeated yet in a Hardmode world, all enemies have a 0.04*1/2500 (0.04%) chance of dropping this item, with the exception of statue-spawned enemies, Meteor Heads, and Old One's Army enemies.