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It was made in a joint effort between Nintendo and St.GIGA, the latter at the time being a popular Satellite radio company. Contrary to popular belief on the internet, Bandai had no involvement with the hardware or servers and is known to have used them only to supply expansion data for their SD Gundam G-NEXT Game.
The Satellaview had features relatively comparable to Sega's Sega Channel service in North America - its most notable feature was the ability to download games, news magazines and articles from St.GIGA's servers. A feature that was highly important, but has not been nearly as well documented, was its ability to stream Satellite Radio. At times this was used to play pop music, advertise, or allow people to listen to radio programs while playing games - for certain special games, particularly the games advertised as Soundlink, of which many of the Mario games showcased on it were, audio was played intentionally to go along with the gameplay and consisted of character voice acting and arranged game music. The service was discontinued on June 30, 2000.
Mario on the Satellaview
These are Mario games released on the Satellaview. Not much information is available, and what there is is sometimes hard to verify, but reputable sites have mentioned these games.
There are also games that are St. Giga-themed in which Mario characters have cameos and/or major roles:
There are also various magazine releases which have articles featuring Mario characters.