In Mass Attack, Repeerc's body starts to decay, Creeper absorbs the radiation through his arm, which adapts to suit it. This turns it into the Mass Cannon. It's default option is a beam that duplicates things, duplicating Jelo and Red Fork before being stopped, but it can be set for things to be added into the top, and duplicated and fired out of it.
Crêper has a dumb version of this, called the Mash Cannon, which fires mashed potatoes.
When Creeper was reverted from his Killer Robot form in The Dream Dimension, the Mass Cannon was destroyed.
- Its appearance is based off of the Tachyon Cannon's appearance when fused with Malware in Ben 10: Omniverse.