I'm looking for some really cool GM ideas/making a GM idea general so that people looking for something cool can find it

I'll contribute a few

1) Having the Torestus mentioned in False Prophets eventually detail how Tor was given the knowledge to leave the planet by summoning a ship from the warp. The idea is that the planet is now a highly populated Hive World/Forge World, and the heretics must sacrifice the entire population to bring out a Grand Cruiser from the warp. Can use Rogue Trader rules for it, maybe introduce space battles in this way? Could also have the ship piloted by demons, so this would be something for heretics with like 80+ infamy. Perhaps then have thier final mission to destroy Scintilla?

2) Infect a PC with the obliterator virus and see if they can RP well enough to survive...

I was lookign for the Obliterator Virus, do they talk about it in the book? Anyway Obliterator arre pretty intelligent and usually a very independent faction taht all CSM must bargain with to have support form them.

The Obliterator faction is a mix between the Traitor Techmarines and the dark tech of the Dark Mechanicum.