Max Flexer is a fitness trainer Demon Beast who appeared in the Kirby: Right Back At Ya! episode "Fitness Fiend". He was downloaded from Nightmare Enterprises by Dedede in order to get back in shape after eating chips enchanted with Pufferzime, a chemical that makes anybody who digests it puff up like a balloon. Max Flexer's training medhods are quite uncomfortable and some even dangerous, such as an electric shock or a treadmill with spikes at the end. But in the end, his medhods worked. Kirby then inhales his headset and gets the Mike Ability and sings an extremely loud song that destroys Max Flexer and causes Castle Dedede to be reduced to rubble.
Max Flexer's name in the original Japanese version of the show is Macho-San.
Max Flexer looks like a traditional fitness instructor. He is, of course, in great shape, since he is a fitness trainer. His hair is curly and pink, he has red wristbands, white shoes, and he wears a retro-style yellow jumpsuit that has a red sripe. He also wears a headset, and has tanned and brownish skin. He has the sunglasses of a stereotypical trainer that nearly always shine. His mouth is even larger than Kirby's, and it is full of pearly white teeth.
- Max Flexer is one of the few Demon Beasts in the show that are seen to be capable of speech.
- He is obiviously a parody of the real life fitness expert Richard Simmons, given his voice, mannerisms, and profession.
- In the Kirby Master mode of Kirby Mass Attack, he makes a surprise appearance.
- In the original Japanese version of the show, when Kirby and Dedede are exercising, Dedede's iconic theme can be heard.
- He is one of the few Demon Beasts that actually do exactly what Dedede ordered them for, the others being Delivery Man, Cold Virus, Hardy, and Paint Roller.
- He is able to get everyone but Meta Knight to dance.
- Max Flexer was voiced by Corey Burton, but he was uncredited for the role.