Arm-Mimic

Arm-Mimics are distinctive because of their large arms. They behave in the same way as Mask-Mimics, emulating every move Link makes. The backstory of these creatures, if they even have one, is completely unknown. The appearance of a Arm-Mimic can be somewhat described as a person and a potato combined into one being.

They are actually fairly strong, normal sword strikes having no effect on them with the normal sword. Stronger swords, such as the Seashell Sword and the Noble Sword are capable of hurting the Arm-Mimics with normal swings. A single touch from them does an entire heart of damage, making them one of the more damaging non-boss creatures in any of the games they are in. Spin Attacks are effective against them, regardless of the sword. As they will copy Link like a mirror, Link is capable of manupulating these creatures into one group. If he moves well, he can ensure that while they cannot touch him, he can come up to them and finish them all in one swing.

Link's Awakening
In Link's Awakening, Arm-Mimic's surprisingly have the strongest attack of any basic enemy within the game. Simply contacting an Arm-Mimic will cause Link to lose three full hearts. Arm-Mimic's are found only within Turtle Rock and a few caves in the overworld. Using the Pegasus Boots along with the sword makes it easier to take out large groups of these enemies.

Trivia

 * By using the Power Bracelet or Power Glove to latch onto a wall, the Arm-Mimics can be manipulated much easier than normal.