Good-Fortune Unicorn

Whenever another creature you control enters, put a +1/+1 counter on that creature.

Mesa Unicorn

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

Brightmare

When Brightmare enters, tap up to one target creature. You gain life equal to that creature's power.

Celestial Unicorn

Whenever you gain life, put a +1/+1 counter on Celestial Unicorn.

Lathiel, the Bounteous Dawn

Lifelink
At the beginning of each end step, if you gained life this turn, distribute up to that many +1/+1 counters among any number of other target creatures.