Knowing you finished this in only two days does mitigate slightly some of my issues, but I'll still make a comprehensive list for you of everything I found. Take this as inspiration to do even better next time!

• The biggest issue would be the infinite flying glitch. If you run, jump, and then spam B to attack midair, then you can just hover in place or fly forwards. I was able to use this to skip entire levels, and even fly out of bounds. Make sure you always apply gravity , otherwise players can skip through entire challenges!
• For some reason, the first level was the hardest. I found that those little flying bug guys with the homing projectiles were the hardest enemies by far, and the first section of the first level is just full of them. A challenge like that should be held until later sections of the game, because it gave me a very hard time for what should've been an introduction to the game's mechanics.
• Sound design! Beeps, boops, and background music are vital to having a game feel complete! Even just some rudimentary sounds for footsteps, dealing and taking damage, and dying would've gone a long way. Next time, make sure you set some time aside for putting a few of those in!
• I'm not sure what this had to do with the theme of light and dark. My first though would be maybe a metaphor for good and evil? But in that case, I'm not sure why bugs would represent the evil side. Next time, I think you should consider the theme beforehand and try and make a game that revolves around a specific mechanic pertaining to the theme.
• Unfortunately, this is not 1-Bit. I'll give you the benefit of the doubt and assume that the bugs' wings are using the alpha channel for its gray colour, but the sawblades are distinct creamish in colour. 
• "B" is an awfully strange button for attack. Any reason for this? I would've thought "Z" or Left Mouse would've been a better button to choose, but that's a minor nitpick at most.

To end on a positive note, I really liked the animations! Especially our little ninja running around was nice to look at, so props to you for that.

Thanks for creating!