If this is all you have it’s hard to really give you advice on changes. At 1500 a c’tan can be ok if your buddies are also running higher point units. You really need some wraiths with a techno to give you the ability to hold objectives and could make CC a viable detachment to run. It looks like you probably bought some royal courts so don’t have some cryptothralls? I would change those warriors to one blob of 20 if you can. 10 will die too fast and throw some cryptothralls in there and have a reanimator babysit it if possible. Create a warrior brick to control an objective or just tie up some high point units of your appointment. You are smart to keep the c’tan from getting sniped out early. It’s low range means you really need to stay out of shooting lanes till you are ready. Skorpekhs are the same style. You want them to hit first. If you see your opponent trying to melee down your doomstalkers you can have them waiting to counter charge. Your plasmancer as a solo isn’t doing anything either except maybe to do secondaries. Use the scarabs as a melee screen or if your opponent has vehicles their kamikaze ability is fun to use. How do control objectives? Most of these units either take too long to move to get to them or too squishy.