Hi, thank you very much for your comments ! It really helps ! here are some answers :
bugs : I definitely need to polish the final "fight". And indeed, a few challenges don't work, will be fix.
gameplay : I like that some mechanics are not explained completely, specially in the end, when the player feel like he master everything. For example, the shield can take damage and break only late in game, once you're already a good player and you know many other tips to survive. The thunder demon remove all your magical power for one turn, but I think it's written in his description ;)
balance : don't hesitate to tell me which boss drops can be improved (removed?), which are too strong (double arrow ? ) ?
Keep working on it ! Thanks a lot !