Alrigtt!!! Dude, this game is fucking lit, well done!
In terms of feedback -- some platforms are super jump-unfriendly, like 1-2 pixels away from being jumpable.
Apart from that, I loved it! I definitely don't feel like you overstayed your welcome, as I really just wanted to bash some more ninjas together!
The last boss took a bit of effort, but again, I didn't feel like it overstayed its welcome.
I really hope you bring this one to life, would love to play a full version of it!