Nice game! With a tidbit of polish, I think you can go far with this concept. Here are my two cents:

• The controls are too sensitive, making it difficult to correctly land on a platform of 1 tile. 
• The player should be able to use the rewind in case they fall in the pit.
• The pit in the entry level, after the mob, does not trigger death.
• In the underworld, you can get stuck under the falling block making it hard to rewind. Could be a bug, could be a feature ;).
• The enemy asset is clashing a bit with the feel of the game.
• It's not entirely clear that jumping onto an enemy kills it.

I hope my comment is not too overwhelming, I really think you got a good concept: it's working correctly and I like the art style. 

Keep up the good work!

Cool game. Was a bit confused at first as when I got to the door, nothing happened. Thought the pit was a trap, and fell in by accident one time when I noticed the key.

A couple quick tips to help you out in the future: Use a capsule collider for the player character instead of a box collider; I was getting stuck on the ground a lot, and I'm pretty sure that's the reason why. Also, create a "Physics Material 2d," set the friction to 0, and apply that to your character or walls; that will make it so he doesn't stick to walls anymore.

As for the game design, I'd recommend slowing things down a lot. The player moves way to fast to react in time to use the rewind mechanic for enemies and pitfalls.

Overall though, nice job; it's a finished game with some decent art and that's pretty cool.