Mayhem Brawler

The achievement is not very difficult, just practice moving the bosses a little and be aggressive, especially with the first two bosses, try to lose as little life as possible on them.
I recommend playing with the Dolphin, which has a lot of damage. What will define whether you finish the mode is whether you can manage the lives and items you pick up during the mode.
Basically, I would recommend that you use healing items when your life is low, and special items when they are empty and there is no possibility of filling them up by giving combos to your opponents.
Play on the lowest difficulty and be careful with the pig-faced boss, as he can damage you while you hit. Also avoid standing in the corner taking hits from the chain guy and be careful with what Nosferatu looks like when he jumps and falls in floor. The last boss, I would recommend having one life left and at least two emergency healing items left in the scenario for the best chance of victory.