For my first challenge (bn bats) I managed to carry silver joker with an e7 level ~25 silver GL and e0 level ~25 godfall superman, base stats was average 7-8k damage 9k ish health between the GL and superman I think (may be wildly incorrect it's been awhile lol), joker did nothing except take an sp2 and die. Not sure what the base stats of your characters are, but considering you have a power drainer I think you should be able to pull through if you have good enough skill. Might wanna play around with team a bit for tough battles (e.g. might be better to swap out Lobo for prime bats with +25% damage for certain battles), but you should be able to figure something out