darkeldar + grey knight allies

I'm pretty sure its OK to take come the apoc as allies as long as they don't deploy within 12". I'm thinking taking a librarian and 10 terminators. I think this would fill assault and psychic phase gap in in my list. They would deepstrike on turn 1 with a 3+. I'm wondering if I'm better off taking a voidraven/missiles, a razorwing, and 5 medusae in a raider or if the 10 terminators and the librarian would make a larger impact in game.

Think its probably best to stick with the dark elder options, Voidravens are an absolute game changer and tbh, taking Grey Knights as allies will probs cause you a bit of a headache, because a lot of people can be very difficult with allies.

In canon terms it isn't impossible for them to be allies however, it is well known that the Dark Eldar hate chaos demons for obvious reasons and if necessary will happily fight alongside Grey knights.

Good luck with your plotting!

What do you mean people are difficult with allies? The idea is that the grey knights are being used to smite the daemons that form as a result the atrocities committed by the kabal. From the grey knight perspective theyre using the dark eldar a daemon bait. Allowing a a few to suffer a fate in the dark city as a benefit to the security of mankind

I have a friend who plays Black Templars and we have done matches as a team, without fail people argue with us that the two would never be allies regardless of any scenarios we give

Well the rule book is pretty clear on allies. That argument would switch me to fine gentleman mode pretty quick

I've never had anyone have trouble with strange allies.

Personally, I think your plan could work quite well. The one thing Dark Eldar have always lacked in my opinion is something to lock the opposing army down. We need to move in fast, but thats made difficult if the other army is also swift enough to get on the move.
So having a deep striking unit turn one, and one that can take a lot of damage itself, would be really beneficial as long as you don't get them too close to your troops (because of the distrusting roll thing).

And if we're talking fluff-wise, the only excuse Grey Knights ever need is "Oh look, Daemons."
They may turn on their allies after the battle (or be complained at by Imperial forces), but thats another game. See the Dameon, kill the Daemon, regardless of who or what they're playing with at the time.

Yeah I'm really going to try it. I'll start with 5 terminators and a librarian and try it out but I'm really thinking I need 10 terminators for maximum staying powrr