I've always enjoyed my personal hc that Blood players would have earth powers, to complement Breath's wind. It makes sense, as Blood IS about material connections and worldly attachment.

I feel like Doom would have fire powers, contrasting Life's canonical plant-based growth. It comes from Sollux's planet. The Land of Brains and Fire has to have SOMETHING to do with its player's aspect, (like Pulse & Haze w/ Blood, Thought & Flow w/ Mind, Quartz & Melody w/ Time), and I can't find an inherent connection between Brains and Doom.

Rage would have just. Purple power??? I don't know, Rage is pretty abstract like Hope. As long as it reads as doubt & skepticism that can make stuff fake, I'm sure it's fine.