Before I get into how he's been re-done, here's a little poem I wrote for him!
All of the le-matoran laughed and sang, work was play to such a joyful gang.
But there was one matoran who wasn't so elated, he sat there in his hut, so very frustrated.
Mariko they called him, with gloom so unrelenting, he sat there in his house, endlessly lamenting.
The other matoran wanted no such company, and perhaps they were overzealous, but this made the young Mariko very jealous.
Twisted and tormented by his loathing for his kind, Mariko delved deep into the jungle, draped in cobwebs and vines.
Though for Mariko the matoran did not worry, when he returned...
They'd all be sorry.
So yes, Mariko is originally a Matoran now, due to the new Anti-Toa laws, which I agree with. But after turning on his friends, somehow he's transformed into the powerful sorcerer he is now.
What are his powers? Well, Mariko's strength comes from his spite against the Le-Matoran, who are naturally fun-loving and joyful. His Powers will reduce his opponents to weary husks of who they once were, drained of all aspiration and energy.
He's meant to be one of 6 Y2 enemies, each toa mach to an individual villain as discussed in the last podcast. Whether or not this'll stick, I don't know.
Of course, eventually Mariko would be defeated by Lewa's overwhelming spirit and energy. He'd most likely fall to his knees (If he has any, leg debates 101) And weep. All he ever wanted was to be like the other matoran, but his hatred twisted him into a vile shadow, and he was manipulated by a greater evil power. Whether forgiven or not, Mariko's in full belief HE isn't the badguy.
They'll all understand, soon...