Here is another idea:
"I know that mobs are two types aggressive and none aggressive. I suggest for a third type, which is a mob who takes a defensive position "active form" when a player entered its range. This mob wouldn't attack the player unless attacked. Also this mob might show some affect when a player gets in his range or zone. for example: if a player entered a dog-like mob range or zone, then the mob might bark till the player leaves or attack the mob."