Thank you for the comments here and on the game page, I'll reply to both here.
I'm really happy you enjoyed the game!
Regarding the keypad tone puzzle. I know that for some people these kinds of puzzles are hard (actually, I'm not great at them either!), so I'm glad I included an option to skip them :D
Sorry about the load button! I wanted to have multiple save slots, so clicking the load button would open another interface. Unfortunately for some reason, the save system stopped working and I didn't have enough time to understand why, so I just had a single save slot as a replacement. I also wanted to have autosaves, but that's another thing I had to cut for time reasons. Hopefully, I'll be able to put these things in in a post-jam update.
For the graphics, I used Clip Studio Paint. It's a really good program that has pretty much everything I need for drawing and animation, but it's a commercial product (although it gets regularly discounted).
I don't have a huge experience with Krita, but heard a lot of good things about it. Plus it's free and can do frame-to-frame animation as well.
Grease Pencil looks cool, but I don't know how suitable is for regular illustrations. I've seen some amazing things done with it, but it also inherits Blender's interface which isn't very easy to use.
By the way, I've yet to play Mervin Pissaro (I've been slacking playing jam games lately :D) but it looks really fun!