Night of the Flying Merfolk is a rare Enchantment — Saga card from Mystery Booster 2 (MB2), collector number 532. Current market price: $0.18, TCGplayer market prices via Scryfall.
Bedtime story (Don't put a lore counter on this Saga as it enters. Put a lore counter on it at the beginning of your end step rather than your main phase. Sacrifice after III.) I — Create two 1/1 blue Merfolk creature tokens. II — Put a flying counter on each tapped creature you control. III — Draw a card for each creature you control that dealt combat damage to a player this turn.