Cliffhaven Vampire

Flying
Whenever you gain life, each opponent loses 1 life.

Epicure of Blood

Whenever you gain life, each opponent loses 1 life.

Sanguine Bond

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

Twinblade Paladin

Whenever you gain life, put a +1/+1 counter on Twinblade Paladin.
As long as you have 25 or more life, Twinblade Paladin has double strike. (It deals both first-strike and regular combat damage.)

Oloro, Ageless Ascetic

At the beginning of your upkeep, you gain 2 life.
Whenever you gain life, you may pay {1}. If you do, draw a card and each opponent loses 1 life.
At the beginning of your upkeep, if Oloro, Ageless Ascetic is in the command zone, you gain 2 life.

Marauding Blight-Priest

Defiant Bloodlord

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

Amalia Benavides Aguirre

Ward—Pay 3 life.
Whenever you gain life, Amalia Benavides Aguirre explores. Then destroy all other creatures if its power is exactly 20. (To have this creature explore, reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Drogskol Reaver

Flying, double strike, lifelink
Whenever you gain life, draw a card.

Nykthos Paragon

Whenever you gain life, you may put that many +1/+1 counters on each creature you control. Do this only once each turn.

Attended Healer

Whenever you gain life for the first time each turn, create a 1/1 white Cat creature token.
{2}{W}: Another target Cleric gains lifelink until end of turn.