Wow, I actually didn’t. I thought Dig with the first one, had it on 3DS.

As I said the only “hidden gem” I know that stayed exclusive to DSi was X-Scape, known as X Returns in Japan and the very generic “3D Space Tank” in Europe (I almost thought it was not released in Europe, it was a surprise finding it under that name).

It’s a sequel to X (a.k.a let’s do a freaking 3D game on the original gameboy), also made by Dylan Cuthbert, who was also one of the main devs on Star Fox. It has that cool retro polygonal 3D style, but with good framerate (that was not really a thing for these games on the gameboy or SNES).