Marauding Blight-Priest

Whenever you gain life, each opponent loses 1 life.

Exquisite Blood

Whenever an opponent loses life, you gain that much life.

Flay Essence

Exile target creature or planeswalker. You gain life equal to the number of counters on it.

Sanguine Bond

Whenever you gain life, target opponent loses that much life.

Whip of Erebos

Creatures you control have lifelink.
{2}{B}{B}, {T}: Return target creature card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step. If it would leave the battlefield, exile it instead of putting it anywhere else. Activate only as a sorcery.

Exsanguinate

Each opponent loses X life. You gain life equal to the life lost this way.

Vito, Thorn of the Dusk Rose

Whenever you gain life, target opponent loses that much life.
{3}{B}{B}: Creatures you control gain lifelink until end of turn.

Defiant Bloodlord

Flying
Whenever you gain life, target opponent loses that much life.

Tainted Remedy

If an opponent would gain life, that player loses that much life instead.