Grigori's Coffin

Grigori's Coffin enters the battlefield with five slumber counts on it. Whenever a vampire enters the battlefield under your control, remove a slumber counter from Grigori's Coffin. When Grigori's Coffin has no slumber counters on it, transform it.
{b}{b}{b}, Return target vampire from your graveyard to your hand
This artifact can be your commander