When I played this game for the first time (a casual playthrough), I got disconnected online occasionally due to a player quitting or a connection loss. Eventually, I actually lost connection while in the treasure room at the end of one of the levels. At first I was really angry, but I soon discovered that the game had counted the level as complete. I decided to go to single player and exit the level in a treasure room to see if it worked in single player too, and it did.

So my question is, should it be allowed for speedrunners to exit a level in treasure rooms to save time? I don't know why this shouldn't be allowed, but I haven't seen anyone else do it, so I don't really know. This would be really helpful for costume-less runs, after all.

Well all costume runs are NG+ and this would only be useful for single player runs unless you do it on the final level of each world with friends as i think once you choose a world, that is the only world you can choose from. Im not completely sure but for a fact it would be slow to do it in multiplayer