Thriving Grubs is a common Creature — Gremlin card from Kaladesh (KLD), collector number 138. Current market price: $0.04 (foil $0.28), TCGplayer market prices via Scryfall.
When this creature enters, you get {E}{E} (two energy counters). Whenever this creature attacks, you may pay {E}{E}. If you do, put a +1/+1 counter on it.