Warden of the Grove is a rare Creature — Hydra card from Tarkir: Dragonstorm (TDM), collector number 351. Current market price: $3.03 (foil $5.24), TCGplayer market prices via Scryfall.
At the beginning of your end step, put a +1/+1 counter on this creature. Whenever another nontoken creature you control enters, it endures X, where X is the number of counters on this creature. (Put X +1/+1 counters on the creature that entered or create an X/X white Spirit creature token.)