Bat Colony is a uncommon Enchantment card from The Lost Caverns of Ixalan (LCI), collector number 5. Current market price: $0.26 (foil $0.16), TCGplayer market prices via Scryfall.
When this enchantment enters, create a 1/1 black Bat creature token with flying for each mana from a Cave spent to cast it. Whenever a Cave you control enters, put a +1/+1 counter on target creature you control.