Thinking back, maybe if it were a Baal challenge and you have to build up to a 1 flick kill all to and including him then the god strength reduction that stacks with UBC would make more sense. I still think a challenge with the reward of the first 9 giving GP then a % chance of all gods dropping double GP could still be a thing. Either way, I'm looking forward to what more Ryu comes up with.
Challenge Idea: Baal Flick Challenge. Double Rebirth Challenge, but rather than beating Baal to win, you have to beat him and all previous gods with one single Flick.
Reward: Something god related. Lower god strengths (stacks multiplicatively with UBC/UAC for P.Baals), GP for Gods under Izanagi and after those first 9 chance for more GP per kill upto some %, or something else entirely.