The final iteration of Superoon, Great Master Superoon was constructed from the damaged Great Superoon and recently excavated parts from doctor Hamstead's latest dig. With the revelation at the end of the last series that the Roog encountered so far were merely scouts for a massive alien invasion, Great Master Superoon's power was needed now more than ever! Henry and Toby were now joined in battle with Valerie who not only handled repair, but controlled the all-important Super Reactor that powered the new machine.
Abandoning the old Missile Mace, Great Master Superoon now uses an ancient technology to generate a guided energy beam mace- the Beam Mace! Fight on Great Master Superoon! Defeat the Roog!Art Notes
This design is an upgrade of the Great Superoon form of Superoon:[link]
Again, with several years of progress, the animators would now be able to make a more solid and slightly more complex design, along with the toy makers.
And as for why:
I've been working on mecha design for my comic work, but I came to the realization that just like the Japanese robot anime series had to build from simpler designs to more complex ones, I need to do the same. I need to develop a mecha style of my own that builds from a simple base.
This is the last iteration of Superoon, for now at least. My next mecha picture will be for a new made-up series, and I will build on what I've learned to make it.