This is a neat concept for a game, and I love the sprites for it (even if they are a tad inconsistent). I do wish there was a little something going on in the background, even a static tileset like the one found in Pixel Survival would have drastically improved the games aesthetics.
But, to the more important aspect of this game, I think the mechanic is really neat! There are only two things that I can think of that would improve it:
1 - Connecting lines. Instead of pasting a square at mouse positions, you should work on implementing a system that stores the mouse points on a list, and have a pen sprite render a solid line through all of those points on the list. Including breaks for bringing the mouse up, and allowing for the line to be smooth can both be challenging elements of getting this to work, but I have a project of my own that uses an image editor like this in scratch that I can show you guys if you'd like. (just dm me on discord (@Faye ⚧), i'd be happy to provide the source code and explain how it works)
2. More methods for refilling ink. Since this is a roguelike, having ink bottles spawn on the ground, or some idea similar to this, I think would improve the quality a lot. Don't get me wrong, I actually really like the idea of killing certain enemies to refill it as well, but currently this system does present a problem:
If not enough demons and projectiles spawn on the stage while the player is running out of ink, it becomes improbable that they will be able to make a comeback. Pretty much every death I had was a result of this. I think implementing a change like this could balance the two difficulty factors (managing ink, while maintaining dodges and reaction time) a lot better. As it stands, managing ink is more or less the sole factor of determining a loss, rather than part of it.
Overall, really creative concept for a cute game, and I'd love to see a full version of it someday! :3