Original idea and very fun game, my best score is 3140.
One bad thing I have to say is that spamming works good, so I think you should limit the healing somehow.
If you'll keep working on the game, I think it will be good to make the enemies randomly spawn and base the score on how much time did the player survive plus with how many knights.
While commenting this I thought that maybe you can also add a shop so that the player will be able to buy or upgrade knights with money that monsters will drop. I feel like this game has a potential to be much better(Its still good now) and I hope you will keep working on it. Nice job.