When Chittering Rats enters the battlefield, target opponent puts a card from their hand on top of their library.

When Gray Merchant of Asphodel enters the battlefield, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Bestow {3}{B}{B} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.) Flying At the beginning of your upkeep, you lose 1 life. Enchanted creature gets +3/+3 and has flying.

Flying When Liliana's Specter enters the battlefield, each opponent discards a card.

When Phyrexian Rager enters the battlefield, you draw a card and you lose 1 life.

When Ravenous Rats enters the battlefield, target opponent discards a card.

Exile all creature cards from target player's graveyard. You gain 3 life for each card exiled this way.

Destroy target nonblack creature.

Tendrils of Corruption deals X damage to target creature and you gain X life, where X is the number of Swamps you control.

Corrupt deals damage to any target equal to the number of Swamps you control. You gain life equal to the damage dealt this way.