Nightmare

"This island is going to disappear... Our world is going to disappear... Our world... Our... world... "-The Nightmares' last words

Nightmares are the main bosses that appear throughout Link's Awakening. Over the course of the game they try to stop Link from waking up the Wind Fish. The only reason they are trying to stop him though, is they don't want their world to disappear which is what would happen if Link did succeed in waking the Wind Fish. It's hard not to feel sorry for them.

Moldorm

File:Moldorm-Art.png

"BUZZZZZ! BUZZZ! OUTZZZIDER!"-Moldorm

The boss of Tail Cave. It is pretty much the same as the boss Moldorm, from A Link to the Past. It is one of the easiest Nightmares.

Genie

File:Genie-Art.png

"HO HO HO! I'm your bad guy this time!! HO HO HO!"-Genie

The boss of Bottle Grotto. This genie isn't the kind that grants three wishes, it's the kind that wants to kill Link! Genie is invincible while in a bottle. It first pops out of a bottle and shoots fire, but after Link breaks its bottle with the Power Bracelet, it goes around the room shooting fireballs at him; although it is vulnerable to Link's Sword during that time. The Nightmare will pop back into a bottle after a few seconds and start the process all over again.

Slime Eyes

File:Slime-Eyes-Art.png

"NEENER NEENER! YOU CAN'T FIND ME! NYAH NYAH!"-Slime Eyes

Slime Eyes is the boss of Key Cavern. Link has to find it by hitting the wall causing Slime Eyes to fall from the ceiling. It can be defeated by hitting its eye over and over using a sword equipped with the Pegasus Boots. After hitting it a bunch of times it will divide into littler pieces.

Angler Fish

"BLOOP! BLOOP! GLUB! GLUB! OGGGH! FOOOOD! BLOOOOP! GLUB!"-Angler Fish

Angler Fish is the boss of Angler's Tunnel. This fish is hungry . . . for Link! He can kill it using his sword or Bow. The battle with this terrible fish is fought in side perspective.

Slime Eel

"Ssso... you are the outsssider, come to wake the Wind Fisssh... KEEE-HEE-HEEEH! I shall eat you!TSSSK, TSSSK!-Slime Eel

Slime Eel is the boss of Catfish's Maw. It is an Eel. Link can defeat it using the Hookshot.

Facade

"Hey dummy! Need a hint? My weak point is... !! Whoops! There I go talking too much again..."-Facade

Facade is a face . . . in the ground. This Nightmare is the boss of Face Shrine. He can be defeated using bombs.

Evil Eagle

"BAH! I'm not going to hold back! I'm going to make you wish you were never born!!"-Evil Eagle

Evil Eagle Is the boss of Eagle's Tower. The interesting thing about the battle with him is the face that it is fought all in side perspective like Angler Fish. He can be defeated in many ways, but the Hookshot works best though.

Hot Head

"CRACKLE-FWOOOSH! You're finished! I will never let you play the Instruments of the Sirens!!"-Hot Head

Hot Head is a flame who happens to be the boss of Turtle Rock. He can be defeated with the Magic Rod. Hot Head is a pretty difficult boss.

Final Nightmare

Main article: Nightmare (Boss)

"We were born of nightmares... To take over this world, we made the Wind Fish sleep endlessly! If the Wind Fish doesn't wake up, this island will never disappear! We would have been the masters of this place... But you had to come here and disrupt our plans! Heh heh! You can never defeat us!!! Let's rumble!"-Voices of the Nightmares

This seems to be the head honcho of the Nightmares. There are six forms that appear throughout the battle: Nightmare of Giant Bot, Nightmare of Agahnim, Nightmare of Moldorm, Nightmare of Ganon, Nightmare of Lanmola, and Nightmare of Dethl. After all these forms are defeated, Link can awaken the Wind Fish.

Reference

All quotes and various info from Zelda Dungeon's Link's Awakening Walkthrough (http://www.zeldadungeon.net/Zelda04-links-awakening-walkthrough.php)