Giant's Left Arm is an enemy in Final Fantasy IV: The After Years exclusive to Final Fantasy IV: The Complete Collection. It is part of the superboss Lost Babil, and is faced in the first part of the battle alongside Giant's Chest and Giant's Head.
The Left Arm will cast Reraise on itself when killed, effectively making it indestructible. It otherwise casts Flare and Firaga, and may cast Fire, Fira and Firaga in sequence. Destroying the Head begins a chain reaction that destroys the Chest and Left Arm.