Ajani's Mantra

At the beginning of your upkeep, you may gain 1 life.

Celestial Unicorn

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

Vigilance
Landfall — Whenever a land you control enters, put a +1/+1 counter on Prowling Felidar.

Whenever another white creature you control enters, tap target creature an opponent controls.

Draw a card, then you gain life equal to the number of cards in your hand.

You gain life equal to the number of creatures on the battlefield plus the number of artifacts on the battlefield.