Angler Fish

The Angler Fish has appeared as a boss enemy in Link's Game Boy adventures. It strongly resembles its namesake.

Link's Awakening
Link encounters this boss in Angler's Tunnel, the fourth dungeon in Link's Awakening. Angler Fish is the Nightmare guarding the Surf Harp. It can use a ramming attack, fling enemy fish at you, and drop debris on you. These are all easy to dodge.

Link fights it under water. Its vulnerable point is esca (fleshy growth resembling a lure) that hangs from its forehead. Slashing rapidly with the sword is most effective, but the Bow and Bombs will work as well. This boss needs very little strategy to defeat and can be killed even before it has a chance to attack.           

Oracle of Ages
Although Link encounters this mini-boss in Jabu-Jabu's belly, the battle is fought on land. The Angler Fish will either jump on top of you or spit bubbles at you.

The best strategy is to shoot it with the Seed Shooter to bring it down, then strike its esca (lure) with the sword. After taking some hits, the fish will repuff and bounce around, shooting bubbles. After several repetitions of this pattern, the Angler Fish will explode.