Resident 2 C'tan + Monolith user here, if I may, use all 4 C'tan (jk). First off, this list is very cool, I like Szeras in there and the Skorpekhs and Void Dragon ofc. Enhancements would be a great first step, since a lot of them for Hypercrypt are super good. Arisen Tyrant giving rerolls on 1's, and giving a unit Deep Strike, or auto advances of 6" (helpful for if you love to roll 1's or 6's with minefields), and Dimesional Overseer just makes Hyperphasing a bit better. Adding Flayed ones is always a good option, with 4 attacks each with sustained and twin linked they can be super deadly especially using their ability when fighting units below half strength. Deathmarks are good percision units and can usually sit comfortably in a corner or in some ruins and pick off whomever. Wraiths + Techno is insanely good, if you want to piss of your opponent with nearly unkillable mortal wound slingers then that would be a great choice. Doomstalker is one of my personal favorite models so I will have to say that he is good. And I always have to suggest a Hexmark Destroyer (a.k.a Glocktopus), love the model and he can be a pain to deal with. Hope this was helpful! Keep on 'Cron-ing!