Matoran would be pretty neat, but if you could add Bohrok?
Like , shift would launch a krana at the opponent, and then you could switch to that controlled character, and use their elements, but not their mask. And a could have the Bohrok attack like Bohrok do (I don't want to say "peck") and the other controls could be the Bohrok elements, or powers and such.
Hordika wouldn't be as cool , because it's basically just having a limited amount of elemental energy, and basically giving the character the ability to shoot webs and such.