I got stuck too. It appears to be straight forward. Hit fireball until they run out of mana then aoe. However I don't have enough mana for that strategy to work. I'm don't know what other moves I can make... : /
I think I found the problem. If you lose a 2nd time against the Willowisp you don't receive the increase to your mana. Therefore, you won't have enough mana for the next area.
Oh really? How can this happen? I'm looking at the code and there shouldn't be any problem. It will take time to fix this, but I can't update the game until the Jam is over anyway.
I found the problem, but I can't upload the fixed version until the jam is over. Fortunately for me , execution isn't rated on this Jam, so bugs shouldn't affect the score haha XD