Ogre Magic, Part 1: Great Maw & Heavens
One of the great things about 8th edition Ogre Kingdoms is that they now have access to some new magic! To be precise, they can now take Lore of Death, Lore of Beasts, Lore of Heavens, Lore of Fire (Firebelly), and their own Lore of the Great Maw.
The Butcher Tax
Similar to Tomb Kings, Ogres have to pay a tax if they want to take something besides Lore of the Great Maw, or a Firebelly. Before you can select Lore of Death/Beasts/Heavens, you must first have a Butcher with Lore of the Great Maw. This means, if your Slaughtermaster wants Lore of Death, you'll need to take another Butcher with Great Maw as well. Because of this, I'm going to be looking at the lores they have available from the perspective of a Level 4, or a Level 1/2.
Lore of the Great Maw
This is the signature lore for Ogres, it contains 4 buffs (+1T, +1S, Regen, Stubborn), a Magic Missile (2D6 S2, ignores armor), an auto panic check, and a so-so Vortex. The Signature Spell causes Stubborn, which can be extremely useful when fighting through some of the tougher units, like hordes of Empire Knights (damn you Damon!), Chaos Warriors, etc. Be careful though, since it is a spell, it's not something you can rely on 100% of the time.
Lore of the Great Maw on a Level 4
On your Slaughtermaster, you are essentially guaranteed to get some great buffs. These can often be augmented to affect all units within 12", due to the Slaughtermaster's lofty +4 to cast, those aren't always that hard, plus you can always 6-dice a big regen spell and make your opponent cry. If you aren't sure about what to give your level 4, this is not a bad choice.
Lore of the Great Maw on a Level 1/2
When you are using a level 2 wizard of any kind, it is very important to look at the Signature Spell. Stubborn, while handy, isn't often a super important spell to have, and will be even less useful in the presence of a Crown of Command. If your level 4 is going for a different lore however, you have little choice. I wouldn't ever take a Level 1 with this lore, since there are too many spells that you might just not want or need.
Lore of Heavens
Similar to Lore of the Great Maw, Lore of Heavens has a lot of utility. Two hexes, one augment, 2 magic missiles, Comet and Wind Blast. The Signature Spell is going to make your ogres harder to hit in combat, while simultaneously making it more difficult for your enemy to pass fear tests (which could put you up to needing 6's to be hit!), plus it can help negate a cannon to boot! The main Hex and Augment from this lore will either let you re-roll 1's, or force your opponent to re-roll 6's, while not huge, this can help against Poisoned attacks a ton, or give you a couple extra hits.
Lore of Heavens on a Level 4
On your Slaughtermaster, you will reliably end up with a magic missile of sorts, Ice Shards, and maybe some extra offense, or another Augment/Hex. The magic missiles are both amazing at eliminating chaff and redirectors, especially so if they happen to be a flyer, and Ice Shards will help keep you alive in combat. If you're playing against a static, or clumped up army, Comet of Casendora is really nice. I typically tend to play an army with few units, so the amount of damage I will take from Comet, is minimal when compared to the enemy. With this in mind, you can often cast it into the middle of the field with little worry. This is definitely not a bad lore for a Level 4, though keep in mind that using this on your Slaughtermaster will mean you wont necessarily have all the great buffs from the Great Maw.
Lore of Heavens on a Level 1/2
The Signature Spell here is Ice Shards, which you may have noticed that I'm a huge fan of. With that in mind, the other spells in the lore (maybe except Wind Blast) are all pretty good. If you need to save points, you can take a level 1 for just Ice Shards and he will be well worth his points, though with the utility of this lore, I would recommend taking a level 2 and subbing the less desirable spell for Ice Shards.
These are both lores with great utility. Lore of the Great Maw is going to be more defensive, while Lore of Heavens will be more offensive. If you're building an army where you want to support your ogres the best you can, then these are probably the lores for you.