Coral Reef is a common Enchantment card from Homelands (HML), collector number 24. Current market price: $0.16, TCGplayer market prices via Scryfall.
This enchantment enters with four polyp counters on it. Sacrifice an Island: Put two polyp counters on this enchantment. {U}, Tap an untapped blue creature you control, Remove a polyp counter from this enchantment: Put a +0/+1 counter on target creature.