Awesome work! I had heaps of fun with this game!
Things I particularly liked:
>The game made me feel like a ninja badass: movement and flow was on point; immediately I felt quite ninja-like, able to move around swiftly and with ease, wall jumping and richocheting my shurikens around felt very cool
>Sound/Audio: I loved the background music, also made me feel badass. Cool sound effects too.
Things that could be improved:
>I think you could have leaned more into the rewind theme: a lot of the time it felt somewhat unnecessary (in the open area at the start the shurikens auto-returned to me it seemed), and when I was using it inside it essentially just was a reload function (albeit where the speed of the reload is affected slightly by how far you threw the shuriken, but that was essentially a non-issue the entire time). Even something simple like having the shurikens deal damage on the return journey too would have made it feel a bit more special.
>Greater enemy variety: This could have been a time thing due to the game jam, but I think having different types of enemies may have mixed up the gameplay a bit. Maybe an enemy with a shield which faces you so you have to ricochet shurikens to kill him; or ones that charge at you and are invincible while charging so you have to jump over them and then shuriken them in the back (just ideas). Otherwise it was mostly effective for me to throw shurikens at range just at the enemy's range.
>Maybe increase the damage of the enemies, and decrease the damage of spikes. I never felt threatened by the enemies really, I still tried to dodge their projectiles, but I probably could have brute forced them. Meanwhile I accidentally bumped the spikes twice which was an instant death each time.
Very minor stuff:
>I missed the first checkpoint the first time round, maybe make it so the player can't miss it (force them to go through a tunnel that its in) so they always activate it and know what it is
>The dash seemed quite weak/unnecessary, maybe beef it up a bit
>When jumping off ramped surfaces it seemed to automatically go into my double jump, meaning i couldnt jump as high.
Overall:
Had heaps of fun! While I would have happily played more, I felt the level size was a good length for a game jam game and it didn't outstay its welcome. Despite the fact the 'Things that could be improved' looks a lot longer in this review that's just because I wanted to be detailed on areas of potential improvement. I still had lots of fun while playing your game and thought you did great work!