One of the featured games from past jams has an endless mode, is it okay if I also add one to my game? Or should I wait for the end of the jam to add an endless mode?
My game, Run Like Dave, also includes an Endless Mode as an optional mode. Players can still choose the 20-second mode if they want a quick session, which aligns with the jam’s requirement for short, 20-second games. The Endless Mode is just an extra option for extended play once the player has mastered the 20-second challenge. I do like your idea of unlocking the endless mode, but unfortunately i ran out of events in Construct to do that and don't want to undo stuff, but if I could I would unlock the mode after collecting a minimum amount of butterflies.
According to the jam FAQ, it’s fine to have other modes longer than 20 seconds as long as the 20-second mode exists as the main experience. So Endless Mode doesn’t appear to conflict with the rules — it just gives players a way to keep having fun after completing the official jam challenge!