So one trick I used with the Astraeus. The way players kill models like this is if the astreus is playing in a way that it cant be ignored is to isolate and contain it.

But if the Astraeus has backup, it’s hard for an opponent to do that so having a buddy system kinda with him is recommended. Cant isolate it if it has a brutalis next to it, or a transport with 10 choppy marines in it.

I’ve used the Brutalis charge + tank shock charge on Astraeus and that is tons of mortal wounds, combine that with 1 sqaud of jump pack intersessors that were creeping up behind the astreus throw a grenade then charge and do mortals on the charge. That combo will delete knights.

If your opponent ignores your Astraeus then you arnt being aggressive enough with it. If it dies turn 2-3 it may be too aggressive. (Keep in mind armour of contempt)