The Nameless Mist

Whenever The Nameless Mist enters the battlefield from anywhere other than exile, exile
it.
When The Nameless Mist enters the battlefield
or attacks, exile target nonland permanent until
The Nameless Mist leaves the battlefield.
Whenever a creature would be returned from
exile to the battlefield, if that creature wasn't
exiled by The Nameless Mist, you may return
The Nameless Mist from exile to the battlefield instead.