A warning for new players. Ice Blast has longer cooldown than Fire Blast and cannot be targeted on the ground. The area of effect is plus-shaped so it's difficult to hit more than 1 monster. Makes me wanna un-upgrade that skill ;(
Don't use popups, they are very annoying and prevent the user from using the rest of the page. It's a showstopper that will prevent people from trying out your game.
Use a text field in the game area. Also you lose all history when all the text is in the dialogs, you should have a scrollable list instead.
After making a wrong decision, I got the message "You died". I would have liked a bit more details... and not dying unpredictably...