The Arm Cannon is a device on which weapons are mounted on, used by Grubs and Armored Grubs in Plazma Burst: Forward to the Past. It is possible to recreate this weapon in Plazma Burst 2 using the Invisible Gun.
This variant fires shotgun like bullets, and it fits in with the Grub's yellow color scheme. Its performance is similar to the Shotgun C-01s.
Standard (Armored Grub)
This variant fires the same bullets as the standard variant, but fits in with the Armored Grub's color scheme. It features only one barrel instead of the two barrels the first variant seemingly has.
This variant looks similar to the standard Grub Variant, but with a different color scheme. It fires a rocket at the same speed as the Marine's Rocket Launcher, and is only used by Armored Grubs.
A variant of the Arm Cannon with blades. It is unused, and would likely serve a similar purpose to standard PSI Blades.