Cool ideas, in my initial scope I had actually planned the zombified versions of the enemies. Having done only the zombified warrior, I realised it would take lots of time to work on the pixel art (which I lacked). I also had a lot of problems with the AI while I was coding it so decided to simplify it.
As for why the Lich is angry, he is angry because a group of buffoons woke him up early in the morning. He is just cranky :D Btw It was written in the last sentence at the epilogue screen as a joke but nobody mentioned it so far :P