Fungus Sliver is a rare Creature — Fungus Sliver card from Time Spiral (TSP), collector number 195. Current market price: $0.77 (foil $5.66), TCGplayer market prices via Scryfall.
All Sliver creatures have "Whenever this creature is dealt damage, put a +1/+1 counter on it." (It must survive the damage to get the counter.)