Oni Wound Healer

As Oni Wound Healer enters the battlefield you
gain 1 life.
Whenever you gain 1 or more life, put a +1/+1
counter on Oni Wound Healer.
At the beginning of your upkeep, you gain 1 life.
When Oni Wound Healer leaves the battlefield,
you lose life equal to the +1/+1 counters on it.