LogFAQs > #971609407

I don't know what Endless is but maybe?

The thing I'm thinking of you had a running health total that tracked through songs and you progressed through a map with stages with songs and difficulties pre-selected and you could pick easy/hard songs as you went through (if you were getting beat down, you might want to pick an easier song on the next stage so you could heal for example), and then eventually there'd be a hard stage at the end that was the "boss"

A lot of the mechanics of the game (the healing in particular) seem like they'd be obsolete without a mode like this so I feel like it probably is what you're saying even if there totally was an "end" to these maps.