Metriod Prime: Hunters.

It was the best FPS, arguably the only FPS, on the Nintendo DS. Nintendo has long since shut down their online service for the DS. However, if you go into your WiFi settings you can change your DNS to point to a server that spoofs Nintendo’s credentials.

Thanks to this exploit you can play all the original DS games online with a legitimate game, on a legitimate console. There’s even a discord for MP:H with a matchmaking channel, clans, and regular tournaments. (The same probably goes for Mario Kart DS)