From the Super Mario Wiki
“Stouter than an iron burrito... Studlier than a snow tire... I am... Wario-Man!”
Wario-Man is Wario's alter-ego in the WarioWare games. Wario transforms into this form by eating some sort of garlic, his favorite food. In the WarioWare games, Wario-Man hosts the last set of microgames the player faces. There are no rules to his games and they all involve Wario to at least some degree. Wario-Man also appears as Wario's Final Smash in Super Smash Bros. Brawl.
In WarioWare: Twisted!, while checking up on Dr. Crygor's production of WarioWare: Twisted! systems, Wario decides to sit down on the assembly line and play a game. He is then tossed into Dr. Crygor's Gravitator. When he comes out, he turns into Wario-Man. When the player completes his stage, he goes back in the Gravitator and gets a power suit, and flies up in space. Meanwhile, Orbulon, Mona, 9-Volt, 18-Volt, Kat and Ana take a cruise on Orbulon's new ship, a yellow Oinker. The Oinker then sees Wario-Man and attacks him. Mona recognizes Wario in the suit. After being attacked, he falls down in the sea near Crygor's lab. Crygor is seen fishing, and he reels in Wario!
WarioWare: Twisted! is the only time Wario-Man's mustache is red. In all other games, it is black.
Wario-Man appears again in WarioWare: Touched!, though how Wario transforms into him is different. In this game, Wario starts to feel sick. He decides to eat some garlic to relieve himself, but the only garlic head left in the fridge is green and odd-looking. Since garlic is Wario's personal cure-all, he goes ahead and eats it anyway. The garlic infects Wario's stomach with viruses, and when Wario's immune system eats the viruses (thanks to the player) the reaction turns Wario into Wario-Man, and he starts to go on a rampage. Later on, Wario-Man is hit by a train and gets knocked all the way into a sewer, where he changes back into Wario, fights the Sewer Guru, and gets hurt by doing so.
This game suggests that Wario-Man doesn't gain many enhanced abilities, as it is shown he can't fly very high or fast, and he has difficulty crushing a toaster and the train that eventually knocks him away. However, it may simply mean Wario's sickness wasn't cured by the garlic.
WarioWare D.I.Y. Showcase
Wario-Man appears in WarioWare: D.I.Y. Showcase, the WiiWare counterpart to WarioWare: D.I.Y.. He helps people open doors to the bathroom. Succeeding one of the microgames will make Wario-Man successfully open a door to the bathroom. Failing a microgame causes Wario-Man to fail at opening the door.
Game & Wario
Wario-Man cameos twice in Game & Wario: in the second stage of a microgame in Gamer, where he must avoid a dinosaur's foot; and in one of the prizes of Cluck-A-Pop, where he is answering the phone after the player dials a phone number. It is notable that Wario-Man refers to himself as W-Man in the latter cameo, rather than his full name.
Super Smash Bros. series
Super Smash Bros. Brawl
Wario-Man is Wario's Final Smash in Super Smash Bros. Brawl. Unlike most Final Smashes, Wario's Final Smash is more of a power-up than an attack. When Wario breaks open the Smash Ball and the Special button is pressed, he eats a hunk of Garlic and gains a superhero suit, that boosts his power and speed by quite a large margin. He is invincible in this state, and will not take damage (unless he goes off-screen, or eats any explosives) or even flinch from attacks. When using his normal attacks, he will hit with extra power, or gain added effects to the moves. His punches will act similarly to a Smash Attack, and his mid-air moves allow him to gain altitude with each move (except his down aerial).
In addition to boosted normal moves, his Special Moves will also gain extra strength and tactics, and a fully charged Wario Waft can almost always make 1-hit KOs (KOing even at 0%), but his added speed will act as a downside when using the Wario Bike, as he will ride it very fast, which can result in falling off the stage. On the upside, however, the power of the bike is also greatly increased. Unlike in WarioWare: Twisted!, his mustache does not turn red, for it is still black.
Super Smash Bros. for Nintendo 3DS / Wii U
Wario-Man returns as Wario's Final Smash move in Super Smash Bros. for Nintendo 3DS / Wii U. He remains mostly unchanged from Super Smash Bros. Brawl, with an exception of a couple attacks. On an additional note, Wario-Man's special moves can't be customized, despite being completely identical to Wario's.
Rhythm Tengoku: The Best+
Wario-Man makes an appearances in the Rhythmware challenge set of Rhythm Tengoku: The Best+. He appears in the final game of the set, Ringside, in which he (replacing The Wrestler from the original version) is interviewed by Mona.
Official Profiles and Statistics
Website Bio from WarioWare: Touched!
What a radioactive spider is to Peter Parker, a particularly nasty old clove of garlic is to Wario. Wario-Man's superpowers are something of a mystery. He's not afraid of chopping a giant's nosehairs, though.
Trophy Information from Super Smash Bros. Brawl
Super Smash Bros. Brawl Sticker Information