Nice twist on Super Mario by having to control two characters at once. It definitely messed with me having to remember which character was being controlled by which input, but that's a good thing.
At first, I thought the point was to swap between the two characters. I didn't realize until I saw a comment about it that both could be controlled at the same time. I think the instruction to use Space to swap gave me the wrong impression.
The player collision was very sticky which made for some frustrating moments. You have to let go of the input to get off of surfaces which can hinder your intended movement. I am also not sure what the intended way to get the checkpoint that is on the high platform in the middle of the level. I ended up reaching it by sticking to and bouncing along the wall, which didn't seem to be intentional.
It was easy to overlook the fireballs that the birds dropped. I would suggest making the art for their projectiles bigger or more noticeable in some way.
I also felt the auto-scrolling camera bit was too slow. I think I would have preferred the follow-style camera for the whole level. A dedicated autoscroll level for later in the game, when the player isn't getting used to the controls still, could be cool.
Overall, I enjoyed what was here and managed to get to the end. It's a fun idea that could use some more polish. Nice job!