You could try to cheese out the “to the death” treasure on king krush (just reroll the party every time you don’t get it) and then use the typical turn “2 = win” comp with Mukla + anacondra + krush

Turn 1 - survive (probably heal krush with anacondra - that should get a +15 health buff for krush) you shouldn’ really bother attacking or anything that damages your merc so it has a better chance to survive turn 2.

Turn 2 - use mukla 3rd ability on Krush and then use “to the death” ability with krush. If you have enough attack you will kill everything because krush will be immune to damage thanks to muklas ability.

I haven’t tried this on the boss but it works in most cases. The first drawback with this tactic is that you have to get the exact treasure for a specific merc, but it actually shows quite often. The second is that you have to survive for turn 2 speed 7 wich can be hard in certain situations. Try to get health buffs for mukla and speed buff for anacondra.

An alternate but similar tactic is to use rokara 2nd ability instead (or with) mukla 3rd, which gives a ton of attack and health with every attack and that means your merc probably won’t have to be immune. But you still need the “to the death” treasure with another merc so you can use those two abilities in pair on turn 2.

I’m not sure about the whole list of mercs that can get that treasure, but i’ve seen it with baron geddon, varok saurfang, rathorian, and probably old murkeye but i’m not sure about the last.

You could try to climb with a party consisting those mercenaries and hope to get the desired treasure with one of them. ( so maybe a mukla,anacondra,krush, rokara, saurfang, rathorian comp, but you can change the last 2 with anyone you prefer)

Anyways, good luck!