For the pixel art I use Aseprite like maybe 90% of people, it's a great tool that does cost some coins but nothing to fancy !
For the art, I like to go for different pixel art syles every JAM and pray the gods of luck to find something appealing. For this one I tried using the smallest amount of pixels per characters possible as I wanted to make the sprite more expressive in a way. This led to a major lack of freedom while animating obviously, so instead of drawing sprite animations I focused on squashing, them and adding meaningful SFX and VFX to make up for it. That's definitely what I like doing, challenge yourself, define constraints on different aspects of your game, and that's when you'll have to be the most creative. Ofc sometimes it does not work out, but when it does, you end up feeling so proud of yourself and in my case, you have a lot of players sticking around and you don't understand why hahaha !