I wrote this plugin for a follower who who runs a server and wanted to let her moderators kill mobs but not use the /KILL command because they were killing things they shouldn't be killing like players' armor stands and item frames.
To kill mobs, issue /SAFEKILL [MOB] [RADIUS] and it will kill all that type of mob within that radius. You can kill specific mobs such as COW or ZOMBIE or VILLAGER, or kill general classes of mobs such as CREATURE or ANIMAL or MONSTER.
The permission node is - safekill. There are no subnodes; it's all or nothing.
To install this plugin, copy the plugin JAR file to your server's plugins folder.