Darkrai

Darkrai is a legendary pokemon which came to the Kanto region to assist in defeating Arceus.

He is cursed, and as a cursed legendary pokemon he is a formidable and dangerous opponent.

In the series, he is behind the network of cursed pokemon who feed off people's nightmares. One of his plans is thwarted by Vergil's Tyrogue, when his psychic bond with Vergil manages to break the sleeping effect and wakes up everyone, who in turn manage to defeat the Hypno in change of the operation.

Cresselia may play a part in defeating it.