When did Ahra fall to Chaos?
I am asking because I am working on fluff peice for background on a missing Legion I want to do. Do we know when (approximately) he left the Eldar? Would it be possible for me to use his betrayel in the time frame of the early crusade?
There have been lots of fan theories, ranging from him being the Father of Scorpions; the founder of the Incubi; Drazhar himself – all three of those things – and quite a few theories that related back to the quote from Realm of Chaos about Eldar Chaos champions being amongst the most powerful of the Gods' servants.
The quote about Arhra: 'The fallen Phoenix who burns with the dark light of Chaos', from the second edition Eldar Codex (reintroduced in the latest Eldar Codex); and that he destroyed the shrine of Asur is precisely everything we know for certain about his earlier (mis)adventures; so he's pretty open to interpretation.
From inference, you can assume that he left pretty early on after the Fall, as the first Phoenix Lord, Asurmen, met the young Karandras while it was still in progress, so to speak (Gav Thorpe's Path of the Warrior), and we can presume that he took over the Scorpion shrine from Arhra while the Phoenix Lords were at least fairly close-knit – the Shrine of Asur was defended (fruitlessly) from Arhra by the original (probably) Fuegan, for example.
Bear in mind that the information is extremely fragmentary and the few snippets are spread all over the place. On top of that, it's all mixed up with myth; much like the rest of the Eldar background!
In short, it's possible to use him as you've outlined – particularly if you invoke some wibbly-wobbly timey-wimey stuff like the warp, the webway and dream sequences :)
That's what I needed to know. I don't think I'll bring him into the story, he isn't integral to what I am thinking of. That might even be an argument to leave him out of it - a character of his stature should probably be more than a plot device I suppose.
I'll find another way to get there!