Hey, game idea is really awesome and although the artstyle looks a bit inconsistent (It's hard to do art when you're a programmer so completely understandable xD), overall the aesthetic is great.
I love how the player model is finn, great choice, and how each level is actually two levels in disguise. It's a great concept! As some others have said, maybe when one character dies, if the other one didn't respawn as well that would feel a lot better.
The controls can be pretty finicky at times, but I struggled so much with making platformer controls as well that I'm beginning to think it's just how everyone's first few platformers turn out. I think the idea is great, but a few small bits of polish here and there and this would've been an amazing entry as well. Still, it's really solid work, and I think it deserves a good rating. Nice job!