OOoh... Well, the idea would be to create some wards around the caster. So, the wards should practically be units who cannot move but can attack. Try the Forgotten One vines. Then, when the caster unburrows set the owner of each ward to Neutral Passive and kill them. It will give you a nice effect. I hope that's what you need.
Burrow trick is that it uses a burrowed version of the Crypt Fiend (just like Robo Goblin second form). The thing is that this burrowed crypt fiend cannot move because it has its movement speed set to 0.
Make your own burrowed version of the Crypt Fiend and make him moveable. Assure that you added the needed Dependency Equivalents (if you worked with metamorphosis before you know what I mean). The problem is that you will be able to see the Crypt when its moving, even though you shouldn't. That'e because of the animation and so, I suggest you consult a modeler for this problem. They need only to tweak the move animation, which is piece of cake.
