Kelvaj, the Pale Hunter

When Kelvaj, the Pale Hunter enters the battlefield, put a +1/+1 counter on each of X creatures.
Kelvaj has all activated abilities of each other creature with a +1/+1 counter on it.
Whenever another creature dies, put Y +1/+1 counters on Kelvaj, where Y is equal to the creature's toughness.