Shadow (This creature can block or be blocked by only creatures with shadow.)

When Faceless Devourer enters the battlefield, exile another target creature with shadow.

When Faceless Devourer leaves the battlefield, return the exiled card to the battlefield under its owner's control.

Flying

When Hypnox enters the battlefield, if you cast it from your hand, exile all cards from target opponent's hand.

When Hypnox leaves the battlefield, return the exiled cards to their owner's hand.

When Mesmeric Fiend enters the battlefield, target opponent reveals their hand and you choose a nonland card from it. Exile that card.

When Mesmeric Fiend leaves the battlefield, return the exiled card to its owner's hand.

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)

When Slithery Stalker enters the battlefield, exile target green or white creature an opponent controls.

When Slithery Stalker leaves the battlefield, return the exiled card to the battlefield under its owner's control.

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.