Well, they made a game where you can make your own microgames (D.I.Y.), and I believe an Iwata Asks revealed it was basically a dumbed down version of the internal tools they had been using, at least for the earlier DS WarioWare game (Touched.) Not sure if that quite answers your question, but I would bet it's some kind of DSL interpreted by a microgame engine.
Re:Super Mario 64 has been decompiled
by AdmiralAsshat on Tuesday August 27, 2019 @09:39AM
(#20809449)
Fun Fact: The minigames of the WarioWare series began life in Mario Studio, the 64DD Japan-only sequel to Mario Paint.[0][1]
[0]https://en.wikipedia.org/wiki/Mario_Artist#Polygon_Studio
(Side-note: I've always wondered how the mini-games in IS's WarioWare series work—whether each game is entirely custom code, or whether they've come up with some sort of DSL for specifying reflex games. If the latter, I would bet that that has a decent genealogy too.)