Heart of the Swarm Campaign- Korhal: Death from Above (Part 2)

When the Psi-Destroyer reactivates, Dehaka will emerge again under your control, this time accompanied by a sextet of roaches.  Make sure to grab the resource drops near him before moving out to the Northeast on this new platform.  This time, Dehaka has the Drag ability that you can also find on vipers, should you have evolved your mutalisks in that direction.  Use it to reach down into the lower level of the platform and haul out the siege tanks so that you can destroy them more easily, and then you will be able to move in on the entrenchments to the East with less difficulty.  Further tanks and turrets wait to the North, accompanied by an occasional marine- take them out, then have Dehaka move up onto the platforms to grab some more resource drops before taking out the power link.  Or don't, it may not be worth your while at this point.

As you take out the platform, another assault will be launched by Mengsk, so be ready with your main assault force to take out the incoming enemy units.  Yet another assault virtually coincides with the loss of power to the Psi-Destroyer, but after that you're in the clear for a bit.  Use this time to assault Mengsk's forward lines and dig as deeply into his base as you can without suffering serious troop loss.  By the time this period of deactivation for the Psi-Destroyer is over, you should have all your buildings to enable production in place and all of your armor and attack upgrades active as well.

With the return of the Psi-Destroyer effect, Dehaka becomes active a third time, with no accompanying primals but with the added ability to Generate Spawns- these are a pair of half-pint Dehaka, dealing the same damage as their progenitor but taking only half as much damage to kill.  Move him out onto the upper levels of the platform and start taking out the Terrans to the North- you will quickly be joined by a set of Primals dropped in from above, though they are highly vulnerable to the various tanks and valkyries that keep appearing and landing on the upper floors.  Operate the twin forces of Dehaka and the primals to sweep North, and then East across the terrain until you reach the raised corner that contains a barracks and a factory.  From here, it's a straight shot North at the power link, which is thankfully not protected by any more units on high terrain.

With the last power link destroyed, Dehaka and his primal brood join you via a vent located near your primary base, and you can use them to bolster your main assault force- this is where you need to just go wild and stomp through the Psi-Destroyer.  With that done, you are ready to leave the aerial platform and head down to the planet's surface.