Oh, now if players aren't against a unified origin, I can easily see one step of Malvan influence being in what they do best, enjoying spectacle...and expanding it further by empowering a smattering of humans but also making them unknown living cameras (To use a crude term) who can be watched and observed at any time, but especially when they battle.
All it takes is one Malvan with a bit of entrepreneurial spirit, a rivalry with that fellow on the moon, and a 'let's genetically alter humans tech kit' and you can have say a dozen (or two) humans with new powers and maybe whole new bodies ,and some of them would be the PCs. Heck, one of the PCs could even be a somewhat sympathetic Malvan (as sympathetic as they get) coming to warn the humans what's been done to them because he thinks it violates the spirit of the arena to have them fighting outside of it or not knowing they are being treated properly as gladiators etc so he will help them.
Or keep it a mystery and each PC is confused on what happened whatever works.
As Malvans love the exotic, it could be quite the team of 'beautiful freaks' to use the term with odd skin or hair, extra limbs ,etc.Or maybe whatever patron is behind this will insist they remain VERY human looking thank you..that's the point, or a mix. Whatever actually suits the players best.
Why you'd even have an excuse for new Psychological complications/disadvantages 'imprinted' by the Malvans to encourage a better show.
A shy young woman with social anxiety remembers two muggers coming for her, a flash of light, and now she's a veritable superstrong lavender skinned amazon with the pscyh lim "overconfidence" or "show off"- That should help her provide a better show.
A soon to retire 60 year old librarian who likes peace and quiet finds himself walking through a door in the library that was never there before, then returned as a very fit age 25 but now with energyblasts, wings and a new Psych Lim "Enjoys a good fight!" implanted.
A wheel chair bound cop, now behind a desk , drinks some odd tasting coffee, and discovers her legs work again, she can also change size at will... but that new psych Lim/complication "Maverick" means its' hard to follow the rules.
And so on.
Meanwhile , Malvan audiences tune in, and enjoy their superpowered soap opera placing bets on which ones will be come heroes, which ones will become villains etc and eagerly make a tailgate party every time their 'earth bound gladiators' get into fights with each other or other superhumans.
Or maybe your players would hate that...
though now I wish my old f2F gaming group were available