Tributary Instructor is a rare Creature — Merfolk Shaman card from The Lost Caverns of Ixalan Commander (LCC), collector number 64. Current market price: $0.39, TCGplayer market prices via Scryfall.
Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.) Whenever a creature you control with a +1/+1 counter on it dies, draw a card.