Blood Artist

Whenever Blood Artist or another creature dies, target player loses 1 life and you gain 1 life.

Ophiomancer

At the beginning of each upkeep, if you control no Snakes, create a 1/1 black Snake creature token with deathtouch.

When Demon's Disciple enters the battlefield, each player sacrifices a creature or planeswalker.

Flying
When Gravelighter enters the battlefield, draw a card if a creature died this turn. Otherwise, each player sacrifices a creature.

When Fleshbag Marauder enters the battlefield, each player sacrifices a creature.

At the beginning of each player's upkeep, that player sacrifices a creature.

At the beginning of the end step, if three or more creatures died this turn, flip Kuon, Ogre Ascendant.

Whenever one or more other creatures die, draw a card. This ability triggers only once each turn.