After killing the first few units, there is a twilight tower and several twilight hags. The Twilight Hags have small & medium knockback, so send a group of swift melee units to distract the Hags and a group of archers to kill them. Alternatively, you can use Mortar Towers to destroy the Hags from afar.
For the next two sections, killing the spawn buildings is your top concern. There are four in this section of the map. The strategy that I like to use is control spells (mostly Curse of Oink) along with a siege unit like Burrowers to kill the Twilight Infestations. After the Twilight Infestations are dead, you can sweep through the section with little trouble. Beware that Rogan Kayle can be a little fiesty and a little reckless in this part of the map, so make sure that you have a lot of healing for him. A couple of Shamans work well. Another way to keep him healed is place a tower behind where Rogan stands by the second orb. He will heal up when he walks back to his spot.
One strategy for this section that can be done with the F2P fire/nature deck is destroy the infestation that spawns vilebloods first. Make 7 or 8 Fire Stalkers and 2 Rage Claws. Walk straight east and have the Fire Stalker attack the southeast mound from a distance. The Rage Claws will hold the big creatures back long enough for the mound to be destroyed. Run the Fire Stalker back to T2 to heal once the mound is gone. Patience is needed to make enough Fire Stalker, but will make this section easy to clear.
This section of the map is essentially the same. There are several Twilight Infestations to eliminate. Use control spells to disable the twilight armies while your army destroys the Twilight Infestations, then run back to your base to heal. There is a Twilight Infestation in the center on the hill which will spawn Twilight Hulks, so destroying that should be your first priority. I used Magma Hurlers and Virtuosos in this part of the map, but units with siege would be pretty nice. You might be able to try destroying the Hulk-spawning Twilight Infestation with Termite Hills from below.
There are two ambushes in this part of the map as well as a Twilight Dragon in the upper-right corner with Leader Immunities.
Hit-and-run attacks with a group of Swamp Drakes can be used for destroying the infestation in the center. Use a group of at least 6, 9 better. Fly in, attack, and fly back south to your power wells to heal.
The Infected Wrathgazer Edit
Sit around and build a large Tier 4 army here, with some melee units and some ranged units. Send the melee units after the wrathgazer while a few of the ranged units destroy the spirits. Each spirit has 850 health. Tempest is one of the best cards for killing the spirits.