Yeah... I actually didn't think about how you could do that.
Well, if you have an obstacle class with a type variable, you could use 3 obstacle objects and change their place to be in front of the player every couple of seconds and then change their type randomly. But then you have to do many, many thing to make it work, like maybe making the amount of obstacles go up as you get better, and that just introduces more and more problems. Yeah. It's just a bad idea for a game jam, I think.