Duskull

Duskull was one of Darkrai's high up minions and has his partner in crime, Elekid by his side.

Background
Duskull was once an A+ student in school on the Floating Islands, his home. He was persuaded by Darkrai to join his team so he did. Duskull was once offered evolution by Arceus but because of his evil deeds the offer was taken away

Froslass's Adventure
Duskull met Froslass when he was planning to steal the elemental orbs inside a giant house where it is revealed that everyone is a toy. Duskull was there when Darkrai's tower exploded, which he survived and went on to do his own evil deeds till he re-joined Darkrai in series 3.