I'm blown away that even though it was made by 3 people, one person was able to code EVERYTHING in the game - that is some serious commitment and pure will. Insanely great job doing this all in 4 days - you deserve every single bit of it.
Some mechanic ideas that would be really cool to see could be a parry mechanic, where you can halt your movement and then you have a chance to deflect a move back at the enemy, a drive rush mechanic where you have a power where you can dash forward multiple spaces for the price of one turn, a Roman Cancel where you have a power that lets you attack again without wasting a turn once you manage to land a hit, a Rage mechanic where at low health, you can have a power that explodes everything around the AOE, a power that can let you teleport through walls and borders of the game (maybe there could be a secret level on the other side?), or a defensive power-up where you're given armor? Either way, I'm sure you have plenty of ideas you guys can iterate on and make your games even better! Good luck this jam - you guys will kill it!
If you're curious about more mechanic ideas, check out some fighting games like Street Fighter 6, Tekken 8, and Guilty Gear: Strive - I'm a competitive player in those games so if you're looking for more ideas check those games out!