Mass fire power. It's only got a 4++ and 4+ FNP, any shot that goes through has a 25% chance of causing a wound. Out of 12 shots one should cause a wound from pulse guns at Str 5. C'tan has T8 if they are take the god shackle. Maybe attach an ethereal for higher LD. Other wise it's vulnerable to tarpiting.
Ps target the crypteks and it will lose its FNP