The Arm Cannon is a device on which weapons are mounted used by Grubs and Elite Grubs in Plazma Burst: Forward to the Past. All Grubs have an Arm Cannon and all weapons used by the Grubs are part of the Arm Cannon.
This variant fires shotgun like bullets, and it fits in with the Grub's yellow color scheme. Its perfomance is similar to the Shotgun C-01s.
Elite Grub Variant
This variant fires the same bullets as the Grub Variant, but fits in with the Elite Grub's color scheme.
Ray Rifle Variant
Rocket Launcher Variant
This variant looks similar to the Grub Variant, but it fires a rocket at the same speed as the Marine's Rocket Launcher. It is designed to go on the Elite Grub.
It is unknown whether or not this variant is actually a sword, or just something else, but it is unused.