Just as others noted, the lag, sorry... I would love to look at the source code and/or the editor view , because a 2d game like this on Unity shouldn't lag like this(i'm not the best code writer, but i think i have learned enough to at least deal with stuff like this). Though there is already one small advice i can give you, a problem with Unity that i have noticed on my own weak laptops all the time: A Unity game can run almost twice as good with just a windows options instead of fullscreen. I don't know why that is, but Unity really hates fullscreen.(talking about the standalone version, i don't know if the same applies to HTML5). But like i said, a 2d game like this should work either way.
The design is top, especially considering the small time frame you had to deal with. The two player characters looked a bit too...how do i say, unique though. They don't feel like part of the same team.(and I get that they are suppose to feel "part of different dimensions" but it's still too different) I also feel no connection from their design to the world, the designs are just too random for that.
For single player controls(which most people would play this as) i would suggest to make it(or at least give the option to) switch between the characters, instead of using two different controls at the same time. It is simply too much(in my opinion) to use two characters at the same time.
The hint how to restart a Level came too late for me. One of my characters died before i saw that notice and thus had to press every key on my keyboard to find a way to restart the game. (and on that note, stepping on the second players head shouldn't cause it to get hurt)
Sorry if all of this sounds too negative, it really wasn't.