Kanluwen said:
TONS of Astartes Chapters have organs that no longer work. The Ultramarines are, as far as I know, the only ones that have all of their organs still functional. That doesn't hold water for me as evidence of mutations in the Raven Guard.
Those abominations that they used for attacking the Iron Warriors' fortress are supposedly the ones that Corax made via his experimentation with cloning following the Dropsite Massacres, which Corax destroyed/took with him alongside of his research when he vanished.
Geneseed lacking in mutations:
1. Ultramarines
2. Iron Hands
3. White Scars
4. Salamanders (their appearance as far as I'm aware isn't a mutation but rather a reaction of their melanochrome to the intense radiation of their planet)
5. Dark Angels
As far the Raven Guard go, it's well established that they have highly flawed geneseed. If you don't want to acknowledge that that's your business, but GW has stated over and over that their geneseed is so flawed that they can't even replinish their numbers at a normal rate.