Well of Lost Dreams

Whenever you gain life, you may pay {X}, where X is less than or equal to the amount of life you gained. If you do, draw X cards.

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.

First strike, lifelink
At the beginning of the end step, if you gained 3 or more life this turn, transform Lone Rider.

Choose a color. White creatures you control gain protection from the chosen color until end of turn.

Whenever you gain life, you may pay {2}. If you do, draw a card.
{3}{W}: Create a 1/1 white Soldier creature token with lifelink.

Whenever another creature enters, you gain 1 life.

First strike, vigilance, lifelink
Aura and Equipment spells you cast cost {1} less to cast.

Whenever you gain life, put a +1/+1 counter on this creature.

Enchant creature
Enchanted creature has "Whenever you gain life, put that many +1/+1 counters on this creature."

Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

When this enchantment enters, exile target nonland permanent an opponent controls until this enchantment leaves the battlefield.