An old wotmania theory of mine - I think Demandred's comment about having an army increases my case:

The Impersonator

Here is the situation.

<blockquote>”Sammael appears to have resurfaced," Moridin announced, crossing the floor and taking a seat.

"Nevertheless, Sammael, or someone disguised as him, gave orders to the Myddraal, and they obeyed, so it was one of the chosen.”

Moridin's jaw tightened. "I do not know," he said at last, reluctantly, he never liked saying that. "but they sent a hundred Myddraal and thousands of trollocs into the ways."

Ch. 3, Knife of Dreams</blockquote>

So, there seems to be some impersonating Sammael. We know that it is not Sammael, RJ has said that he is gone.

<blockquote> Question: It has been reported that you have confirmed that Sammael died at the end of A Crown of Swords. Could you confirm that you have said this and elaborate on whether Rand was correct?

Answer: Mashadar killed Sammael. Sammael is toast!
Wotmania FAQ</blockquote>

So, we know that it is not Sammael, it is someone impersonating Sammael. Furthermore, we also know that it has to be a forsaken.

<blockquote>Becoming one of the Forsaken involves receiving a mark from the Dark One in return for your oaths; this mark is invisible and cannot be sensed by another human being, even another of the Forsaken, but it can be by certain non-human creatures, including Myddraal and draghkar among others. This may play a part in the Myddraal's obedience but doesn't explain it completely.
Question of the Week No. 6 – Answer to question about gholam</blockquote>

Whoever ordered the shadowspawn would need one of these marks in order to successfully order such an invasion – especially since it involves going into the ways, which hasn’t been too kind to shadowspawn. This is further confirmed by Moridin’s thoughts above. We’ve seen other marks like this, but they don’t seem to be sufficient.

<blockquote>The mark that Alviarin received from Shaidar Haran was not the same as that given to the Forsaken, though it shares one function: Shadowspawn will recognize her as belonging to the Dark One. They will not obey her as they will the Forsaken, however, but she doesn't have to worry about one trying to kill her, either.
Question of the Week No. 2</blockquote>

So far we can narrow it down to one of the surviving forsaken. Aginor/Osan’gar, Rahvin, Bel’al, Asmodean, and Sammael are dead and gone. We can also eliminate Moridin and Aran’gar from the list. We see from Aran’gar’s point of view that she didn’t do it, and Moridin mentioning it in the first place pretty well eliminates him. So, this leaves Mesaana, Semirhage, Moghedien, Cyndane/Lanfear, Graendal, and Demandred.

I argue that we can safely eliminate Cyndane and Moghedien because they are mindtrapped to Moridin. This seems to be too big of a betrayal for them to get away with it. Semirhage has her own plot to keep her busy, and I would further argue that Mesaana is still too shaken up from her ‘encounter’ with Shaidar Haran to undertake a scheme of this nature. This leaves us with two viable contenders for the impersonator – Graendal and Demandred.

Graendal

At the time of the forsaken meeting in the garden, Graendal has no real motivation for action like this. Rand has not yet begun his plan of sending his armies to Arad Doman. Graendal’s base there is unthreatened. Also, this kind of action really does not appear to fit well Graendal’s personality or style.

Here are the comments Graendal makes in the garden.

<blockquote>"That hardly seems possible," Said Graendal as the all moved to take chairs. Her gown was dark gray now, concealing everything. "He must be dead."
Ch. 3, Knife of Dreams</blockquote>

The reaction seems genuine, and she appears surprised. Of course, this is Graendal, and she can manipulate – her gown did turn to a neutral color. However, I don’t see any indication that she was involved.

Demandred

Demandred is the most mysterious of the forsaken. We’ve seen him only a handful of times, and never really seen him act. During the AoL, he was the shadow’s greatest general. I believe that Demandred has spent his time marshalling the shadow’s armies and planning the invasion that we should see in Book 12.

Throughout the series we’ve seen debate among the forsaken as too how much of LTT’s memories Rand has. Demandred has a need to find out if the Dragon Reborn is a simple shepherd from the current age, or if he is indeed LTT reborn with all of those memories. To discover the degree to which Rand has LTT’s knowledge and how he will react to a large army of shadowspawn, Demandred impersonated Sammael and ordered the shadowspawn to attack him in the manor in Tear. Now Demandred can better plan his strategy for the invasion to come, and if Rand had died in the attack, Demandred would have been quite happy.

Here are Demandred’s reactions to in the garden.

<blockquote>"He could never have borne staying hidden this long," Demandred put in, lounging into his chair between Semirhage and Mesaana, legs crossed as though they were perfectly at ease. That seemed doubtful. He was another who was unreconciled, she was sure. "Sammael needed to have every eye directed at him."

"That sounds like Sammael," Demandred said thoughtfully, twisting his goblet and studying the swirling wine, "Perhaps I was mistaken." A remarkable admission, coming from him. Or an attempt to hide to being the one who had worn Sammael as a disguise…
Ch. 3, Knife of Dreams</blockquote>

Aran’gar’s thoughts certainly indicate that we should consider Demandred a suspect. I argue that they are not a red herring, but a true hint.


In summary, it was Demandred who impersonated Sammael and ordered the shadowspawn army to attack Rand. The goal of this was to test Rand’s reaction and knowledge to better plan for the larger invasion to come.