Designing and Planning Action in Games

I can imagine how it's supposed to be in my head, I get the feel down. I know what people will play in my mind. I write design details. I know specifics. But... I don't know how enemies are supposed to act in response to the player, how to give the player breathing room but also make the enemies aggressive enough to pose a threat. I guess this question only applies to action games, though.

I just wonder how to write down or record enemy movement and attack patterns in a way that can be...

Designing and Planning Action in Games