Well, not much to be said about the MOC - he looks good. Not very special but by no means bad. I feel like custom limbs would be nice to have should you consider to work more on him, but this MOC really shows how easy it is to make simple stuff look good with CCBS.
While the liftarms on the lower legs maybe don't look perfect, I really appreciate that the lower legs are covered all around. It's also nice how the staff is so simple but just looks good.
As to backstory stuff: His assigned region should be "none", and I would ask you to elaborate a bit in his backstory. I guess you could say that the Toa team he absorbed were his Toa Hagah, for example.
Otherwise I'm just going to make up stuff I need for his backstory myself eventually.
Change the assigned region part and write down why he absorbed the whole Toa team at once (in the case they were his Toa Hagah he of course absorbed them following Teridax's orders to kill all Toa Hagah)
Then I'll accept Zirolius.