Waves of ultralisks (Sector 1) Edit
13 or 14 waves of 3-5 ultralisks in each, spawning in the Sector 2 beyond the Roach Hill.
This wave is spawned by killing 5 out of the following 7 buildings: The hatch north of the base, The greater spire, The lair, The other hatch, The spore canon and spine near the ramp to roach Hill, and the ultralisk cavern. The game checks every 15 second to see if this condition has been triggered or not. To be exact, you also need to clear the hatch with heal on it inside your base and the hatch above it.
Waves of purple Ultralisk / Small useless weird high headed things. (Sector 1) Edit
Weird almost useless things on every difficulty except oldschool. A lot purple Ultralisks and Spines there. They appear from drop pods - in case of Ultralisks from Nydus north of your base.
This is triggered by walking into the area before the Roach Hill on Sector 1.
Primal ultralisks and queens (Sector 2) Edit
7 or 8 primal ultralisks, 5 or 6 primal queens and some other primal units.
They are spawned as you fight your way through the Roach Hill 1st high ground. Walking past a certain point on the hill will trigger them. As you hear the warning about a large zerg force, get out of there or you'll die. Don't try to fight primal ultras as Predator, as your priority for them is lower only comparing to Cpt Smoker (and other Odins). Thus, Planetary Fortresses don't save you and the strength on this stage is not enough to fight them.
Roaches on the Roach Hill (Sector 2) Edit
Several hundreds of roaches.
The roach spawn here is the same as the ultralisk one, and will spawn once you've killed 4 out of 7 building/units. These seem to be The roach warren on the hill, the brutalisk, the hyldralisk den + evo chamber towards the middle + some of the sporecrawlers and one of the spines on top of the hill. Some buildings in the area around the lair with 3 Ultralisk caverns do also work to trigger this.
The game checks every 37 seconds to see if this condition has been met or not.
Primal ultralisks (Sector 3) Edit
5-6 Primal ultralisk will have a chance to spawn when you kill the following buildings: The 3 ultralisk dens, the lair, the spore canon OR, very rarely, the spore canon in front of levi's entrance. This trigger is not active on Hellwalker.
Waves of mutalisks (Sector 2) Edit
Tens of groups of 7-8 mutalisks.
They are spawned in the top center of the Sector 2 as you kill the hatchery and start proceeding to the top towards the corridor leading to the Leviathan.
They can push a lot of the base if ignored. Be careful with straight tanking them. If you can't get 30+ armor, you'll perish pretty quickly if muta count grows. Not sure if you can kill them fast enough.This trigger is not active on Hellwalker.
Final wave Edit
Starts with tens of primal ultralisks. Continues with giant banelings, giant roaches, giant primal queens and giant primal ultralisks. Finishes with tens of hybrids.
Spawn is timed from the moment the Hybrid General appears. The timing around 9 in-game minutes.
Focus on killing green ultras, as they quickly chew their way through literally everything and will wreck whole base within minutes if not stopped.
On Hellwalker you get a new wave of Deathpenalty bosses and Hybrids when Odins reach the entrance of the hybrid base.