Mayhem Brawler

You need a 100 hit combo for this. On Level 7 (taking the path where you choose to go after the sorceress), you can easily get this fighting the zombies at the start of the level. If you get hit, just pause and restart the level. Just be aware that getting a hit will 'break' the combo, so if you see a fist above a zombie, stay away for a few seconds until it vanishes.

If you are about to get hit, press Y to do your special attack. That's about it, good luck!