BURROWED UNITS
Author: Daktakpaklak

In the early game, sending out Overlords is a great way to discover the location and race of your enemies, and to watch over key choke points so as to be warned of a rush.  As the game progresses, however, it becomes more and more of a risk to allow your Overlods to stray far from defenses.  After a few minutes, and especially when playing against a Terran player who's Marines can fire at air units early on, its a good idea to replace your scouting Overlords with burrowed Zerling.  Burrowed units serve well as cloaked observers to warn of incoming attacks.  And Zergling are cheap, costing only 50 minerals for two.  Having advanced warning of an oncoming rush is a big advantage in the early game.

When you've stumbled upon an unoccupied resource node, burrow a Zergling there.  They'll provide intelligence as to whether or not its safe to expand.  And if someone else decides to move in, you'll be the first to know about it.

Bury multiple offensive Zerg units close to the resources at an expansion node.  As soon as an enemy's worker begins construction, unburrow your units and nail it. He looses his worker and the money it cost him to begin the building.  Be warned: a smart player would first send a unit to observe the area, but until the middle game or unless they send an Overlord, they'll be unable to detect your burrowed units.  If your opponenet sends an escort of troops with his worker, don't worry; allow him to build around you.  Because your units are so close the the resources, you'll end up with workers trotting over the heads of your burrowed units.  Create a diversion somewhere else to draw your enemy's attention away, unburrow your units and nail the workers, then re-burrow them.  This tactic is usually safe, because many players forget to leave defenses or build detectors inside their base.  It's a great way to grind an enemy's economy to a hault.  Think of the surprise your opponent will experience when he realizes   that all his workers have been executed and he doesn't know how!

It is impossible to construct buildings on top of burrowed units. If you burrow units in the right places at an expansion node, you can prevent the enemy from building their Command Post/Hatchery/Nexus.  When they try to build on top of your burrowed unit, they'll get an error message disallowing the action.  Only units with the ability to view burrowed Zerg units will recognize why.  Most of the time, units sent to expand will not have this ability, and even if they execute your unit, you'll at least have had time to muster a forcie and attack the fledgling expansion.

When burrowing large numbers of units, stack them on top of each other. If an enemy dectector should happen along, he'll be able to identify only the top unit. You can have a huge force appearing as just three of four burrowed units! Even better, you can mask the presence of higher-tech units by burrowing  Zergling directly on top of them. The only unit an enemy will see see is the Zergling!