Umbris, Fear Manifest

Umbris, Fear Manifest gets +1/+1 for each card
your opponents own in exile.
Whenever Umbris or another Nightmare or
Horror enters the battlefield under your control,
target opponent exiles cards from the top of their
library until they exile a land card.
If I am mad, it is mercy! May the gods pity the man
who in his callousness can remain sane to the hideous
end!