First appearing in Ben 10: Destroy all Aliens back in 2012, the Retaliator is actually a Galvan and Azmuth's father (wearing a Galvanic Mechamorph armour). The Omnitrix starts going crazy again and starts downloading stuff. Azmuth travels to Earth to try to fix it, though his father doesn't agree after being separated for so long with Azmuth being on Xenon. One Azuth reaches Earth, he disguises his ship as a lorry, but comes in contact with a hoverboarding Ben and a malfunctioning Omnitrix, turning Azmuth into a feral To'kustar. His dad, wearing Mechamorph armour, follows in an attempt to kill the To'kustar, thinking it killed Azmuth.

Although the armour pumps up the user's aggression, it also gives the user Galvanic Mechamorph abilities, such as merging with machines. With Azmuth again on Earth trying to figure out what's wrong with the Omnitrix and why it won't work near Fusion Gwen or Fusion Ben, it would make sense for the Retaliator to return to find Azmuth and protect him from Planet Fusion. And if he doesn't appear as an NPC, his powered-up armour would look cool as a Guide set for Ben:

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