As far as I understand, you want simple game that has hard but addictive gameplay. Similar to Ketchapp games. Repetitive gameplay that makes you want to reach highscore and collect those coins in order to buy different skins. There can be many types of ninja, skin can even change background and whole concept, but same gameplay. I imagine collectibles as shurikens. Would be fun to also have challenges, daily, weekly and as you complete them you get titles like expert ninja, but you start as rookie.
I once made prototype of similar game when I was starting with game development. I can make prototype in few hours and send you to check how does gameplay feel.
I would use Unity for development. Also, I would change jumping from one planet to another, I would toss in mechanic where you need to aim as you are firing bow. With finger slide back at desired angle and power and then release. And add more juiceness compared to Amazing Sheriff game, with simple animations and particle effects. There are a lot of things that can make that kind of game more enjoyable and fun to play. Also i would suggest to go with pixel art, but I leave that for you to choose.
If you are interested in more of my opinion, please e-mail me. :)