Moldorm (Link's Awakening)

Moldorm is the Nightmare of Tail Cave, the first dungeon in The Legend of Zelda: Link's Awakening.

Strategy
Use the Roc's Feather to jump to its tail and strike it with the sword. When it's been hit once, it will go into a frenzy, so dodge a lot with the Feather to avoid being pushed down a pit, which will result in the battle having to start over again. It is very smart to use the spin attack here -- Charge up the spin attack, jump near its tail and let go as you land. After its tail has been struck repeatedly, it will blow up, allowing you to retrieve the Full Moon Cello, the first Instrument of the Sirens.