It's a 2d action side scroller remake of the first Risk of Rain game including some enemies and characters from the 3d release Risk of Rain, which you could consider the second game in the series. It's a pretty fun roguelike to play the main appeal is that once you play long enough you feel like you become a god only to get one shotted by a random mob 2 hours into your play.

https://riskofrain.fandom.com/wiki/Risk_of_Rain_Returns