Right, second post of the day. Dark Angels Librarian coming up.
The Librarian is the cheapest way to fill up a HQ slot, coming in at the same price as a base Chaos Lord or a base Warboss. Additionally, there's not much reason to upgrade him with things like Melee Weapons, Ranged Weapons, Special Issue Wargear or Chapter Relics, so he still remains pretty cheap.
The Librarian can take Pyromancy, Telepathy, Telekinesis and, here's the kicker, Divination. You're paying under 70pts for access to the Divination table. That's a fantastic bargain.
It gets better too. You can pay to make the Librarian a level 2 psyker, and after this upgrade, he costs the same as a Rune Priest. They are actually very comparable. They both cost the same amount, they both get 2 rolls on the Divination table, but whilst the Rune Priest gets a 4+ nullify on all psychic powers within 24”, the Librarian gets to cast 2 psychic powers per turn and still gets to use the 5+ Deny the Witch if his squad is targeted.
The only other option that's really worth considering is the possibility of exchanging Power Armour for Terminator armour. However, it is a little spendy, 30pts for the upgrade, so I'd only do it if your Librarian is your Warlord. If you are taking 2 Librarians (and I can't blame you if you do), then I'd only consider giving it to the one that is your Warlord, it just helps to safeguard that Slay the Warlord point a little more.
So, that's pretty much it for the Librarian, he's fantastic value for the access that you get to Divination. But how is he used most effectively? First of all, it is imperative that you stick him in a squad, this way he can't be single out by missiles and what have you, making him much harder to kill.
Another little trick is if you put him in Terminator armour, and you come up against a Chaos Space Marine list with Heldrakes, is to put your Librarian in Terminator Armour at the front of the squad, tanking the wounds on his 2+ save, but remember to start look out sir-ing them back into the squad if you are reduced to 1 wound, it's better to lose a few marines than to lose your Warlord.
The best way to use Divination effectively is generally to stack the Librarian with the Heavy Support choices. Prescience works fantastic with Whirlwinds, it doesn't matter if you're firing indirectly, as I have the re-roll to my scatter die and so am likely to hit anyway. It's also good to take a Devastator squad. Many of the Divination powers effect the psyker and his unit, meaning that they're most useful if you've joined the Librarian to a Devastator squad. For example; Perfect Timing.
Another way to use him is in a very similar way to a lot of Space Wolf lists. For your HQ, take Azrael, then take Guard allies with a 50 man blob in there, whack Azrael in there to give the squad the 4++ save, and then put the Librarian in too. If you get Forewarning as either of your powers, then you can just swap it for Prescience. Even a roll of a 1 on the Divination tree is good with a blob, 50 models firing at full BS as overwatch when charged is nothing to be sniffed at, even if they're just Guardsmen.
Now that was a quick post. I also think that is it for today, the Chaplain and the Interrogator Chaplain shall come tomorrow.