Ruth, Guardian of Soft Steps

Cats you control have haste and +1/+1.

Whenever a Cat enters the battlefield under your control, put two +1/+1 counters on Ruth.

Whenever a Cat would enter the graveyard under your control, you may pay {3}. If you
do, keep it on the battlefield with a -1/-1 counter. If the Cat's power would be 0 or less, exile it instead.