Fishliver Oil is a common Enchantment — Aura card from Arabian Nights (ARN), collector number 13†. Current market price: $8.65, TCGplayer market prices via Scryfall.
Enchant creature (Target a creature as you cast this. This card enters attached to that creature.) Enchanted creature has islandwalk. (It can't be blocked as long as defending player controls an Island.)