The duel
The gargoyle that’s been watching you from the wall this whole time would like a word. Turn-based. You have two moves and some HP.
Cut to a staged two-character tableau. Your marble sprouts a proper pair of eyes, acquires hit points and two moves, and squares off against the gargoyle that has been sitting on the wall watching you fall off things for the last minute.
Turn-based. A menu. Three or four rounds. Physics: off — not adjusted, not locked down, off. This mode shares zero systems with the game hosting it.
That’s the whole reason it exists. The mode contract was designed early specifically so this would be possible, and it was built last so it could prove the contract in the most obnoxious way available. If a marble roller can host a turn-based menu battle, it can host a rhythm game, or a fishing minigame, or whatever the next idea turns out to be at eleven at night.