hi all i  have a question, how often would one find eldar with mutations? i am sure the answer is "almost never" how ever my group is about to encounter a lost eldar craft wold that has been slowly sinking into the center of the vortex for the last few thosand years, the way i am going to set this up is that the party meets a lost eldar youth that has tenticals for fingers or some such. and he asks them for their help. i am wondering just how other peaple in the area would react to this, and if i should move it to some sort of random wilderness scene instead.

I don't see a problem with this. Eldar can be corrupted, so go with it!

First off, a caveat, I could be completely wrong about this. My understanding is that most of the Eldar during the fall were absorbed into Slaanesh, the exodites and craftworld eldar only surviving due to their distance from the epicentre and perhaps the discipline of the early paths. Dark Eldar on the other hand survived by supplanting their dwindling soul-flames with the pain and agony of others to satisfy Slaanesh. My guess that Eldar could and would suffer mutations, but the closer and longer they are exposed to warp energies the more they would either succumb to what the Dark Eldar became or they would have abandoned the world outright if they were craftworld Eldar. I think looking up some information on "The Crone Worlds" of the old Eldar Empire might give some general insight if you're wanting that too.

Aesthetically and fluff-wise, it just won't do, mutant Eldar. Just not :)

I would assume that most Eldar that get corrupted enough to spout mutations are snagged by Slaanesh on the spot.