It's going to be a challenge having a rotten day after seeing this. I love that you have him squeezing out of a Game Boy screen. I almost missed that little detail which would have been shameful on my part considering how often you've mentioned your love of Wario Land.
"I planned to add more, but I was running out of space..." Yes, I noticed a lack of Wario-Man. He's studlier than a snow tire, you know! Outside of that, not entirely sure what else would be necessary for a complete representation of the legendary fellow. Maybe something like his costumed appearances in Mario Party or perhaps you were thinking about his inclusion in other spin-off games, like Mario Kart or the sports titles. There's more than enough eye-garlic here to take in and enjoy without them.
"Heck, I'd even go as far to say that Wario felt like a more proper rival that Sonic, but that's just me." He definitely is. Sonic is suppose to be the faster one who keeps going forward and Mario's more acrobatic and keeps going higher, but both can do what the other is offering with enough practice. Wario, however, is just an entirely different experience from Mario. Why have style and respect when you can just overwhelm something with brute force and mock it afterwards?
"Also just in case, I did draw Waluigi's cap letter wrong." Wario has done much worse to his friend/brother, so I doubt Waluigi would be too upset by this mistake. He'd still be upset though.