Thank you for recognizing the visuals! I love making art so it means a lot to me.
Regarding the dynamic difficulty, I completely forgot about that area, and it seems that long sessions of gameplay does not reward the player (even enough). As for the i-frames, I'm not really familiar with it so I'll search it for a while; I'll do something about the pesky Japanese goblins' knockbacks to Yuuka.
Generally, thanks for the feedback!