He will spawn if one uses the Skeletron Soul . This item can be crafted from 99 bones, a textile merchant - voodoo doll , a mechanical skeleton head15 Soul of Light and 15 Soul of Fright ! This is the Super Hard Mode version of Skeletron . The boss has 100,000 HP and has 6 arms : one to shoot laser, a chainsaw arm, a gun arm , one to shoot bombs and two where the hands of fireballs come out . Has he lost all poor , he goes into his second form , the laser , Cursed Inferno , bombs and Ichor beam shoots as it rotates . If you have defeated him standing there : Time to end this! and a perfectly ordinary Skeletron with 5000 HP spawns . If you have both , the day comes immediately . His Drops: Ultima Skeletron drops 30-50 Soul of Ever Fright , 50 Hallowed bars and he can drop to 5:2000 a Ultima spell of  damage , and 7 mana per use shoots . The Skeletron ( the normal ) drops but only 10 souls of fright . Boss Music: Boss 7 Music (from the Lunar Boss)