Conclave Mentor is a uncommon Creature — Centaur Cleric card from The List (PLST), collector number M21-216. Current market price: $0.34, TCGplayer market prices via Scryfall.
If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on that creature instead. When this creature dies, you gain life equal to its power.