Lethal Vapors

Whenever a creature enters, destroy it.
{0}: Destroy Lethal Vapors. You skip your next turn. Any player may activate this ability.

Crawlspace

No more than two creatures can attack you each combat.

Carth the Lion

Whenever Carth the Lion enters or a planeswalker you control dies, look at the top seven cards of your library. You may reveal a planeswalker card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.
Planeswalkers' loyalty abilities you activate cost an additional [+1] to activate.

Koskun Falls

At the beginning of your upkeep, sacrifice Koskun Falls unless you tap an untapped creature you control.
Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Ward of Bones

Each opponent who controls more creatures than you can't cast creature spells. The same is true for artifacts and enchantments.
Each opponent who controls more lands than you can't play lands.

Liliana, Death Mage

+1: Return up to one target creature card from your graveyard to your hand.
−3: Destroy target creature. Its controller loses 2 life.
−7: Target opponent loses 2 life for each creature card in their graveyard.

Death Pits of Rath

Whenever a creature is dealt damage, destroy it. It can't be regenerated.

Silent Arbiter

No more than one creature can attack each combat.
No more than one creature can block each combat.