Reserves of the Deserved

Returnal (You may cast this spell from exile and only from exile)
Whenever Reserves of the Deserved or another creature enters the battlefield from exile, put a +1/+1 counter on it.
At the beginning of your first combat phase, detain each creature without a +1/+1 counter on it. (Until your next turn, they can't attack or block and their abilities can't be activated.)