Mobs flee from the attacker when get hurt

[betterworld-sjq]

So some ranged mobs would flee a certain blocks to regroup their positions when shot by the player, not just stand there and only flee when you get closer. This would additionally discourage players' ranged cheezing

complement：
1.It would be better to control the type/source of the damage.
2.Can be combined with animal-like group fleeing feature, like the hurt mob would warn his surrounding allies and make them flee as well