There seems to be a bug in the way endless mode currently works with how it spawns in obstacles.Sometimes, a barrel or a see-saw will spawn from the left and shoot across the screen, slamming right into your biker.
Hey, thanks for reporting! I noticed this too, they were going absolute haywire at times :---) I tried to fix this in the new version 0.3.5 by making the obstacles spawn fresh instead of teleporting them. I still have to do some testing, if it works properly now, but I think it's better now!
