Necron Monolith with 2 squads of Necron Warriors will spawn at the middle relic once any unit (including infiltrated Gretchin) reaches it. Monolith has 8k health on insane. Gorgutz will be teleported there and you will get Shoota and Sluga Boys squad on the site too. Crull will escape northwest but you can't follow him that way as there is barbed wire. Exploration of map is reset at this point. Not long after first monolith a second one with the same support will spawn northeast near a crashed ork plane. It will stop to destroy titan weapon while Necron Warriors will march to your base. Third monolith will land right next to southern imperial outpost at the foot of the titan.
There are 2 crashed ork planes, one northeast of titan that does nothing and one near the western corner where you will get Killa Kan, Shoota Boys squad and ability to create Looted Tanks.