What is Steve in the screenshot?

Not quite, the mod uses "Mr. SyS" for the name as well as made up an acronym (being "Steal Your Soul"). "Mister System" is a more literal interpretation of his name while still being a small reference to the MM mod, but without the forced creepy factor since it directly connects to the Nintendo Entertainment "System"

There are a few acknowledgements to the MM mod, but the Rivals pack is meant to be a celebration to the NES console, like the previous comment says

you do know that the name mr. system literally comes from mario's madness, right? i respect the choice to distance your pack from being strictly related but denying it to the point of not even naming the game in your comment is a little ridiculous lmao

that's alright i can just play it in the background.
sorry bout that but it's just a banger to hear.

Stage already has 8 tracks from several NES games. And this mod pack is meant to celebrate NES history/gaming using an obscure pull, not being connected to that "singing game" aside from a brief usage in his victory theme

think you could add "Unbeatable" too?

Love the CRT filters, they really complete the vibe. Great stage!