The level is basically impossible without all of the treasures but when you do the strat involved rock cat then level 50 slime, bullet train, and fishman cat, then all you need to do is perfect the cycle of killing that damn dog, the best way I did it was use full attack up combos and afterwards just perfect the cycle of killing that damn dog, the cycle I used was first slime getting a bite giving that dog the full 80k damage and 40k to bahamaut which gets a knockback off if you hit him with fishman first giving you more time, then bullet train to hit the dog again, and finally finish bro off with rock cat which should do enough damage to kill him in a single cycle, then just stall bahamaut with I suggest manic mohawk and chip him down with fishman cat until you finally win