If a nontoken creature would enter the battlefield and it wasn't cast, exile it instead.
11/7/2014 Containment Priest’s last ability won’t affect any nontoken creatures that were cast, including ones cast from unusual zones such as your graveyard.
11/7/2014 Containment Priest’s last ability doesn’t stop creature tokens from entering the battlefield. It also doesn’t affect creatures that were already on the battlefield.
11/7/2014 If Containment Priest enters the battlefield without being cast, it won’t exile itself.
11/7/2014 If Containment Priest enters the battlefield at the same time as other creatures, its ability won’t affect those creatures.