This tutorial will teach you how to add a runner headcrab or "Lightning Dog" to the map, and allow the runner headcrab to revive zombies.
Create a test room. Insert a npc_headcrab_runner
Create a Navigation Mesh. The Runner Headcrab should now be able to walk around.
In order to allow it to revive entities you have to enable NPC Properties > Can Be Revived on each npc_zombie that will be able to be revived. You can also use Reviver Group in order to specify which runner headcrab can revive which zombies.
Compile and run your map, and you should have a working Runner Headcrab along with zombies that can be revived.