Flash
If a nontoken creature would enter and it wasn't cast, exile it instead.
Some protection requires a bit of finesse.
(19/03/2021)
If Containment Priest enters the battlefield without being cast, its ability won't exile itself.
(19/03/2021)
If a noncreature card wasn't cast and is entering the battlefield as a creature (due to an effect such as that of March of the Machines), it will be exiled. Conversely, if a creature card wasn't cast and is entering the battlefield as a noncreature permanent (for example, Heliod, Sun-Crowned with insufficient devotion), it won't be exiled.
(19/03/2021)
Containment Priest's last ability won't affect any creatures that were cast, including ones cast from unusual zones such as your graveyard.
(19/03/2021)
If Containment Priest enters the battlefield at the same time as other creatures, its ability won't affect those creatures.
