I am really happy that you like it :D
I had the same problem with my Turn Based Battle System too, after checking for health = 0 I just checked if it is above 230 or some high number because the gameboy cant use negative numbers. Be sure to not set your enemies health to something higher than 230 though. Also make sure that, if the enemy has 1 hp left, the damage is not higher than 25 ( 1 - 25 = 231, if more than 25 the enemy will not be killed but gain a huge amount of health)
Edit: After reading this post I thought I have written it a bit unclear hope you understand me lol