Yeah, something is up with JJ #2.
There's no question you need to reach level 2 in order to defeat the boss. Without reaching level 2, the highest attack damage you can attain is 10, which will require hitting the boss 8 times to win. Even with last chance, you'd need to be able to tank four hits from the boss to pull this off. This means you need 41 HP, which is not possible since there is no way to increase your HP in this puzzle.
So you need to find a way to teleport into the "spectator" area to kill the monsters there and reach level 2. This can be done by trading places with the last imp, getting petition, using LEMMISI to reveal everything, then drinking your potion. You can also head up and grab your shield at this time. You can then teleport in, slaughter the imps, then teleport out with your level-up mana.
Now, from here I'm still stumped. I can attack the boss exactly once before he kills me, after which I can attempt to last chance (no luck) and potentially get another hit. I had to explore everything to reach level 2, so there's no way to heal mid-combat. In any case, to get through that 79 HP titan I'd need to hit him five times in total, which would actually be feasible if I had 1 more max HP and last chance succeeded (mighty hit , hit , last chance, mighty hit , convert BYSSEPS, hit , WEYTWUT, hit ). However, I can find no way to do either, so I'm lost.
It looks like it might be possible to grab chaos avatar, but to get enough piety you still need to get into the spectator area and slaughter them. The problem is that JJ hits you with corrosion and two layers of curse because you aren't purchasing petition, so I can't find any attack combo that works. Due to corrosion, the imps deal 3 damage a hit when I'm cursed and 1 damage per hit when I'm not, so I really can't afford to fight through more than one layer of curse. There may well be some obscure attack ordering that works here, but I can't seem to figure it out. If this is the intended solution, I'd strongly advise the devs to rework the puzzle because victory and defeat hinges on abusing foreknowledge regarding the random seed.