Wow, a very difficult game! I was unable to make it past the Oni. Anyway, I've been a fan of this slowing down mechanic since Megaman 11, so I was happy to see it used here. Landing on the arrows is a really cool idea and very thematically appropriate. The controls were generally easy enough to control, my jumps were controllable and my character moved at a good speed. The music was also nice and picked up in intensity at the right moments.
Some feedback:
- Checkpoints please. It was a nice touch to unlock a shortcut to the boss, but the run back was still a bit annoying, especially with that big hole you have to fall down and climb back out of (where the sword is found). I really wanted the lady who talked about her onsen to offer me a checkpoint then and there.
- The game needs iFrames. The amount of times that I got knocked between arrows and spikes in rapid succession or bounced between oni boulders was pretty frustrating.
- A nice UI touch would be to put some sort of indicator closer to the player to show how much longer they have on the time slowdown. A bar abov ethe head like in Megaman might not be the most appropriate, but I didn't really want to look up at the top left of the screen while focusing on whatever I was slowing down time for. The time slowdown also felt like it depleted very quickly, I think a little bit more leeway would have been nice. It looks like it can be upgraded to more bars later, but I never made it to that point. :(
Overall I think it's a really cool concept and the theme is a fun one to explore. There are a lot of neat little touches here too, like arrows sticking into the walls. If you're going to continue it I'd focus on ramping up the difficulty slowly rather than going full speed ahead with it, but I'd be happy to give a future version another play. Nicely done!