Tainted Remedy

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

Sanguine Bond

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

Plague Drone

Flying
Rot Fly — If an opponent would gain life, that player loses that much life instead.

Carnival of Souls

Whenever a creature enters, you lose 1 life and add {B}.

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.

Kenrith, the Returned King

{R}: All creatures gain trample and haste until end of turn.
{1}{G}: Put a +1/+1 counter on target creature.
{2}{W}: Target player gains 5 life.
{3}{U}: Target player draws a card.
{4}{B}: Put target creature card from a graveyard onto the battlefield under its owner's control.

False Cure

Until end of turn, whenever a player gains life, that player loses 2 life for each 1 life they gained.

Heliod's Intervention

Choose one —
• Destroy X target artifacts and/or enchantments.
• Target player gains twice X life.