Hajime Nagumo (From Common Job to Strongest In The World); after story only
Riderman (Kamen Rider)
Barret Wallace (Compilation of Final Fantasy VII)
Inspector Gadget (Inspector Gadget)
Hoss Delgado (The Grim Adventures of Billy & Mandy)
Franky (One Piece)
Scorpion (Marvel Comics)
Phineus Phibes (Shaggy & Scooby-Doo Get a Clue!)
Ustanak (Resident Evil 6)
Venom Snake (Metal Gear Solid V: The Phantom Pain)
Ashley "Ash" J. Williams (The Evil Dead series)
Cee-Lo Green (Teen Titans Go!)
Experiment 150 "Clyde" (Lilo & Stitch)
Agent J (Men in Black: The Animated Series)
Belle (IDW's Sonic the Hedgehog); only her hands
Warp Darkmatter’s (Buzz Lightyear of Star Command) cybernetic arm has a variety of weapons that are similar to Star Command or it can morph into illegal weapons like a flamethrower, a plasma cannon that fires powerful energy beams, and occasionally from a hand with sharp claw that can slice through space objects mostly metal or often used as a regular/normal arm/hand. His robot arm can also fire bombs from its shoulder.
Wild Dog's (Time Crisis) robotic arm contains a machine gun, a flamethrower, a missile launcher, a grappling hook, and a tractor beam.
Riderman's (Kamen Rider) cybernetic arm can be used for a mace, scythe, scissors, claw, drill, and a machine gun.
The Ustanak's (Resident Evil 6) robotic arm can be swapped out for a telescopic claw, a chain gun, a flail, and a drill.
Alex Murphy/RoboCop's (RoboCop) attachable weapon arm can be used as a machine gun, rocket launcher, and flamethrower.
Death's Head (Marvel Comics) possesses a liquid metal right arm that can morph into claws, blades, a plasma cannon, and a "Cranial Disruption" that allows him to download an opponent's mind into himself.
Phineus Phibes (Scooby-Doo)
In addition to its primary machine gun function, Barret Wallace (Compilation of Final Fantasy VII) can swap his gun arm for a robotic hand, as well as a drill, a pair of scissors, a chainsaw, and a laser.
Scorpion's (Marvel Comics) robotic tail comes equipped with a stinger, a laser, an electric generator, mace gas, and an acid shooter.
Justimon (Digimon) wields the trinity arm which can fire lightning, cut enemies, or become more powerful.
The T-X's (Terminator 3: Rise of the Machines) arms contain, among other things, plasma cannons, flamethrowers, and buzz saws.
Venom Snake's (Metal Gear Solid V: The Phantom Pain) robotic left arm has a variety of different customizations and functions, such as an active sonar, a stun rod, a rocket punch in both lethal and non-lethal variations, and the "Hand of Jehuty," which allows him to snare enemies and draw them to his position.
Over time, Ash Williams (Evil Dead) has performed multiple modifications to his metal hand, such as a rocket punch function...