I would play it as the assassin is revealed - ie - you place the model down.
Only if you win the roll off with the DE player.
As already stated the wizard goes "Theres a nasty assassing in that unit" - then marksman with the HLR goes "alright, hes mine BANG". Just as similar as a wizard saying "Theres the other wizard with all the dispell scrolls" - then the marksman with his HLR foes "alright, hes mine BANG". Surely thats the idea of the item?
Now you're claiming knowledge by intent. That's a no go area.
I can just say "Surely the idea of the item is to give you an idea of the magic items he has, and knowledge of where they are?"
And best thing is.
"Sniper, that unit has an assassin!"
"Which one is the assassin?!"
"The one which looks like the rest of them!"
Before you go "but what about combat? Why bother revealing if he looks like any of them?"
Well, I guess the large circle of dead bodies, and beyond that a "keeping a respectful and fearful distance" bunch of Delves from the one doing ninja flips and throwing Str7 shurikens and knifing down combat lords, makes someone stand out from the crowd, and once he's start doing that crazy shit, everyone watches takes note, aims, and prays he shoots that Delf down before he gets to him.
(Plus if he wasn't revealed in combat either, I'd love that. Invisible and Invincible lord of awesome who adds insane amounts of ASF attacks to his unit! Or he'd be utterly useless as he'd never be revealed, ever!)
Disclaimer: Seriously, you'll at -best- get the Delf player to agree to a roll off, at worst, he'll call you a cheater and not play. Unless he really does like being walked over when it comes to any form of rules disagreement.
Edit: Unless you are a Dark Elf player, then I weep for my kin.
Just post another post, don't edit yours to respond to mine
Anyway, viable tactic and bending the rules deliberately/loop hole rules lawyering are different things. And this smacks of it to me.
