So aside from America's Cleverest Legacy, the ARG's pages have shown us numerous potential promo characters. I think it'd be fun to speculate on what powers such promos would have.
First, Omnitron-U
https://greaterthangames.com/omnitronu
Being a creation of Unity, I think his power would focus on his Components and equipment -- possibly a power that pulls one out of the trash?
And the 80s Rock Prime Wardens
https://greaterthangames.com/timevtime
As a group, going by the cover image, they seem generally angrier, so I'm going to imagine they're somewhat damage based. Then again, the Prime Wardens of our 'verse seem to love supporting each other, so maybe that plays into it?
Argent Adept is the front man, and one hallmark of 80s rock is smashing guitars -- so for him, I imagine a power like, "Do X melee damage, where X equals the number of instruments in play."
Fanatic is rocking the Tina Turner look, so maybe something with sonic damage? Perhaps modified by her teammates in some way?
Haka's the drummer, clearly. Dude is into percussion. Maybe a power so that, til the end of his next turn, every time he does melee damage, he does additional Sonic damage?
Tempest -- electric guitar. I could see him adding a lightning element and/or boost to others' attacks.
Unfortunately, I've never played with Captain Cosmic and thus can't really speculate on how a new power would affect his deck.
And then there's these guys
https://greaterthangames.com/bethegate
I'm really not sure how they would play -- I've never used half the characters in the mash ups, so y'all can speculate on those.