Diregraf Colossus

Diregraf Colossus's last ability won't trigger when you cast it because it's not on the battlefield yet.

If Diregraf Colossus enters the battlefield from your graveyard, its first ability will count itself among the Zombie cards in your graveyard. Similarly, if it enters the battlefield at the same time as another Zombie card enters the battlefield from your graveyard, the ability will count that other Zombie.