Concentration Camp

Whenever a creature enters the battlefield under an opponent's control, detain it. (Until your next turn, that permanent can't attack or block and its activated abilities can't be activated).
“Our policy is one, which is called by an Afrikaans word 'Apartheid'. And I’m afraid that has been misunderstood so often. It could just as easily, and, perhaps, much better be described as a policy of good neighborliness." -Hendrik Verwoerd