Fungus Sliver is a rare Creature — Fungus Sliver card from Time Spiral Remastered (TSR), collector number 203. Current market price: $0.57 (foil $1.16), 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.)