With this character (especially when using a 2000 pt army, in which he will take up your only Lord option) it all depends on which enemy you are facing and the tactics you plan to use.
It is best practice to deploy a general (which should be Alith Anar - if you're playing a 2000 pt game) close to the bulk of your army so it can benefit from his leadership.
Alith Anar has a leadership of 10 so is ideal for leadership tests but the problem is that he's not really designed to lead your army into battle.
Alith is a scout and benefits from the special scout deployment rules which allow him to get up close (in a sneaky scout way) to the enemy.
Mr Anar also carries the Moonbow which is, in effect, a 36 inch bolt thrower but remember his ballistic (or bow) skill is a whopping 7 ! So he's nearly always going to hit the enemy.
Because of this Alith should really be trying to flank the enemy and fire down their files (especially Dark Elves who will have to take a panic test if they suffer any casualties)
Also, thanks to his Shadow Crown, he and his unit are more likely to survive a rout from losing a combat resolution because his pursuers have to half their pursuit movement.
Couple this with the Stone of Midnight which gives him a 4+ ward save and, importantly, makes his unit more difficult to hit with missiles (-1). Together the Stone of Midnight and Shadow Crown make him an ideal leader for a large Shadow Warriors (scouts) unit.
All in all I would not recommend using Alith Anar as the general of a 2000 pt army because you would either lose the benefit of his excellent leadership by deploying with scouts or you would lose his scouting benefits by depolying near the main body of your forces. I might use him in a 2000pt army if fighting Dark Elves due to his and the Shadow Warriors permanent hatred of them.
I would consider using him in a army of 3000 pts or more as leader of a large 20+ Shadow Warriors unit.
His pts cost is 245 which is reasonable only if you make the most of his scouting abilities in a large Shadow Warriors unit.
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