|This is the original Codicier Ignatius, from way back in the day.|
Before I discuss Librarians, it seems like a good place to discuss the Sanguinary Discipline.
The Primaris power is Quickening, which gives the psyker or a character within 12” Fleet and +D3 Initiative and Attacks. I don’t see this being used on Librarians too often, though Librarian Dreadnoughts and Mephiston can make great use of it. This will be tremendously useful as it turns your nastiest character into a verifiable monster.
Fear of the Darkness forces an enemy unit within 12” to make a Morale check with a -2 modifier. I like this power for pushing back important enemy units, which will help prevent enemy counter-assaults and push squads off objectives. If you are aggressive enough, you can keep your opponent in their deployment zone and force units to fall back off the table.
Unleash Rage gives a unit within 18” Rage. If it already has Rage, it gets +1 Attack. There’s nothing bad about this power.
Shield of Sanguinius gives the Psyker’s squad a 5+ invulnerable save, giving it a bit more protection. This isn’t huge, and will be more of a desperation move when you have to charge a squad full of power weapons or are facing down a bunch of plasma guns. It’ll help but is unlikely to make a massive difference.
Blood Boil is a warp charge 2 power, and is an 18” focused witchfire. It makes a single model take two toughness tests, and it loses a wound with no saves of any kind for each one it fails. If the target is slain, it explodes with a large blast with S4 AP5 and Ignore Cover. This power won’t be great for doing damage to tough units, but it seems designed to murder objective holders and win you the game. That large blast will mangle many infantry squads sitting on an objective, and focused witchfire allows you to place the template in the position where it will do the most damage. It’s situational but far from useless.
The Blood Lance is a warp charge 2 beam power, with S8 AP1 and Lance. It gives your Librarian some very good anti-armor firepower.
Wings of Sanguinius is also a warp charge 2 power cast on a friendly Infantry unit within 12”. The unit immediately moves up to 12”. They can’t assault that turn, but it will help get your unit into threat range that much faster. It will even give Terminators the speed they need to get into assault.
The Blood Angels Librarian is very similar to the standard Librarian, but can take powers from the Sanguinary, Biomancy, Daemonology, Divination, and Pyromancy Disciplines. I think Sanguinary does a great job supporting an assault oriented Blood Angel army, but the other Disciplines can certainly be useful depending on your army.
The Librarian is a cheap HQ choice, and I can’t think of a reason not to make him Mastery Level 2 and give the first Librarian you take Gallian’s Staff. My main complaint with Librarians is that they simply don’t generate enough Warp Charge dice to cast powers against many other armies out there (I’m looking at you, Eldar, Grey Knights, and Daemons). Against armies with more reasonable numbers of Warp Charge dice, the Librarian is not only useful but a lot of fun.
The Librarian Dreadnought has become an HQ choice, rather than the Elite choice it used to be. Unfortunately, this means that you can no longer use it to increase your Warp Charge pool. Beyond that, it’s a WS5 Dreadnought with front armor 13. It comes with a power fist with a storm bolter (which can be upgraded to a meltagun or heavy flamer) and a Furioso force halberd (which is basically a power fist with Force, though it’s not a specialist weapon so he won’t get an extra attack. He can be upgraded to Mastery Level 2 (and why wouldn’t you?) and take a Drop Pod.
If you really need a tough psyker and you don’t mind that he can’t hide in a unit, the Librarian Dreadnought can be a decent choice, though the standard Librarian is a cheaper way to get psychic powers if that’s all your after. If you want to go Dreadnought heavy, you can take two Librarian Dreadnoughts and three Furiosos and drop them all on the enemy. That’s a massive amount of AV13 to deal with.
Mephiston, Lord of Death
Mephiston is not the mini monstrous creature he was in the last codex, but he still probably has the strongest statline of any single marine. He lost a point of Weapon Skill, Strength, and Toughness, and two points of Initiative and Wounds. Transfixing Gaze was also toned down, being both harder to get off and doing less. He also costs 75 points less and is now an Independent Character, so it’s not all bad.
He still wears artificer armor and carries a plasma pistol and force sword. The sword is his biggest weakness, as it means his excellent attacks will still mostly bounce of 2+ saves, so you’ll have to choose his targets carefully. He has Fleet, which will help him get off charges as long as he’s alone.
Mephiston is a Mastery Level 3 psyker, and always comes with a unique power, Sanguine Sword. This warp charge 1 power increases his Strength to 10, making him an excellent vehicle killer. He can even wipe out Knights with little problem. Sanguine Sword isn't part of any discipline so, like Force, it won't interfere with psychic focus. His Warlord Trait is Soulwarden, which means it will be very difficult for the enemy to cast psychic powers on him.
Despite his toning down, Mephiston is still a brutal assault character. His main weaknesses are his inability to pierce 2+ saves and his relatively slow movement. He’ll definitely need a transport, and will do very well in a Land Raider or a Stormraven. He can also be used as a counter-charge unit, should you take a more static section to your army that would benefit from his psychic support.