Ever since Wario got that package he's been getting tons of ideas for making WarioWare more successful, with his VR game idea as just the start. And at first it's great! They're doing better than ever, and some of the ideas even help him and Waluigi get their finances in order and move into a freaking penthouse! So things are looking up.
Except...
Except some of the ideas don't feel like his own.
Except he's gradually becoming colder and more businesslike.
Except he keeps Conveniently Forgetting to take off his Meta Glove when he's not using it.
Because the arm is programed similarly to SMG4's old demonic keyboard, but it's far more subtle and insidious since it's not dealing with a sleep-deprived perfectionist already in the midst of a complete mental breakdown.
And it's so subtle that even as Wario realizes that something's wrong with him, he doesn't figure out what until it's too late and he's a prisoner in his own mind.
Now it's-a Metario Time, and he activates a similar program in the replica Meta Gloves to forcibly hijack the minds of the WarioWare crew, Waluigi, and new hires Amy and Mira, then leads the resulting Army in an assault on the Showgrounds, which is the big cliffhanger before what I'm calling WAHtfiWare.
Speaking of which, the format is that Tari manages to convince Metario to settle things with a gaming competition, with both of them using their unique abilities to pull their respective Crews into a WarioWare game. The transition screen between challenges is a fighting game-style character select, with the SMG4 Crew's side being blue, Metario's side being purple, and the real Wario trapped in a TV in the middle. The actual challenge skits are much shorter than usual, both because they're supposed to represent Microgames and because there are a lot of characters and if we went with the standard format we wouldn't be able to use them all even if we included some 2v2-or-more-challenges.
To differentiate him from the real Wario, Metario wears the same suit and bowler hat as the TV Adware guy and his Meta Glove, which looks just like Tari's arm but refitted to Wario's proportions, purple glowy bits instead of blue, and Wario's signature blue "W" on the back of the hand instead of Tari's wing emblem thing. The rest of the WarioWare crew also have Meta Gloves fitted to their proportions, and their eyes glow the same purple as the glowy bits when they're under Metario's control.
Just before the climax song starts, the Crew discovers that they can break Metario's control by getting rid of the Meta Arms when they manage to do so to Waluigi, Amy and Mira. Then during the song they gradually manage to free all the WarioWare employees (coincidentally in reverse order of their debuts Because Thematics) while Metario transforms his in-game sprite (because keep in mind that with how his and Tari's special power works their bodies are still in the real world unlike everyone else), and near the end Wario finally breaks free of the TV and gets to lay an extremely satisfying smackdown on the asshole program that stole his body.
In the aftermath, it turns out that Metario's ideas weren't actually as good for the company in the long term as he thought they were, because as good as the program was it was still working with Wario's brain, so a lot of the extra revenue they got has to go into damage control and the Wario Bros can't actually afford their penthouse. But when they think they're going to have to go back to living on the side of the road, the two Crews have a surprise for them.
Apparently the initial WarioWare VR concept, the one idea that was genuinely All Wario before the Meta Arm had any influence, was the one that actually properly worked, and between the sales from that and everybody deciding to pitch in something of their own, they managed to put in a down payment on a house for the brothers. It's not particularly big or fancy, in fact it's just a 3D version of Wario's dinky little run-down shack from the actual WarioWare games, complete with the big dumb "W" sign on the roof.
And as far as the two of them are concerned, it's perfect. Better than the stupid penthouse even. Because for once in their lives they've finally got somewhere that feels like home, given to them by the first people beyond each-other who've ever felt like family.