I had a lot of fun with this! I love the concept of day/night and the combat feels good, the health bars are a nice touch. The style is visually pleasing although there are a few visual inconsistencies (the frog's pixels are smaller than the ground tile's pixels for example).
I did feel that the slipperiness of the movement made a few bits of platforming overly difficult but otherwise I enjoyed the challenge. I think the game could really benefit from some kind of items to pickup and a scoring system, but otherwise this is a great start, nice one!
(I think the flickering blue lines between the tile sprites can be solved by adding an outline of pixels around each tile as a kind of padding, although don't quote me on this!)