Pokemon Riddle #2

I inhabit the space between waking and sleep,

A guardian of nightmares in shadows so deep.

With a tattered cloak and a ghostly white crest,

I banish my foes to an eternal rest.

On the night of the moon, I emerge from the black,

Once you enter my dream, there is no turning back.

Who am I?

Hint: I am a darkness/shadow type pokemon