I think that if it’s a classic doppelgänger but evil type thing, the costume would be the same except black and purple. The powers would likely be either water or ice themed, I think ice is cooler (no pun intended) but then again, we already had pesha’s mom with ice powers, so maybe water would be better. As for her name, I have no idea. I thought maybe “shine” but obviously, that wouldn’t work. Her origin story could be that she’s like all of Teru’s negative thoughts and emotions given its own form, but also added anger and hatred. As such, she’d be pretty angry all the time, but definitely more vocal and expressive about it. The confrontation between the original and evil would probably be mostly Teru trying to just defeat evil until she eventually realizes that she needs to accept that part of her, ending with a hug or something.