In a Nutshell; The Lore of Nurgle

Lore Attribute(s):

Children of Nurgle (Daemons of Chaos):
If a spell from this lore causes one or more unsaved wounds, choose a unit of Plaguebearers or Nurglings within 12"of the caster and roll a D6 for each unsaved wound caused. For every roll of a 5 or 6, add another model to the Plaguebearers. For every roll of a 6, add one base of Nurglings. These new units have no upgrades and they do not count towards victory points. The placement works the same as the Tzeentch attribute. Considering that Nurgle is the most popular and easily the most useful of the Chaos Gods, I can really see this helping keep that anvil unit of Plaguebearers up for an attrition game that will make your opponent tear his own hair out in frustration.

Bloated with Disease (Warriors of Chaos):
For every spell you cast from the Lore of Nurgle, roll a D6. If you roll a 6  then the caster gets +1 Wound and +1 Toughness for the rest of the game. In any other army, this would be practically an auto-win. However in this army, it's not as needed as it may seem. See, Warriors of Chaos can take casters with armor so that usual problem of worrying about your caster getting shanked by even rank-and-file troops. However, if you are playing an opponent who uses a lot of Snipers, Assassins, Death Magic, etc. then this is really nice to have on any of your casters. It's pretty nice, and the spells in this lore are pretty decent overall, so I can really see this being used to make just insanely tough characters.

Signature Spell: Stream of Corruption
A Direct Damage spell with a casting value of 7+ that uses the flame template at the base of the caster's front base with the larger end placed over the target. All models covered by the template must pass a Toughness test or be slain with no armor saves allowed. This spell is really nice to have, because it's like a shotgun you can hide behind your back that you can pull out and then use to just scythe through infantry. One of the problems you can run into as both Daemons and Warriors is that you will find yourself rather susceptible to being tar-pitted. This is a great way to circumvent that issue. It's also really nice to have with the rising popularity of the Witch Elf horde. I give it a 3 out of 5, and a recommendation to hold off before switching for this spell, because there are some really good spells in this lore.

Spell #1: Miasma of Pestilance
An Augment spell that I really think confused itself and is actually a Hex spell that was adopted by Wyssan's Wildform. It has a range of 18" and a base casting value of 5+. Until the start of the caster's next magic phase, all enemy units in base contact with the targeted unit have their Weapon Skill and Initiative reduced by 1 (to a minimum of 1). This spell can be boosted to reduce the enemy's Weapon Skill and Initiative by D3 (roll once and apply that result to all enemies) for an increased casting value of 10+. This spell seemse pretty mediocre until you remember that you're playing Nurgle. Your opponent is already at -1 to-hit, so dropping his Weapon Skill is like peeing in an open wound of a dying man. As for dropping I, that's pretty nice but against Elves and other stuff like that it kind of loses it's luster. It's also pretty damned cheap to cast, so it's a spell you can use to draw out a Dispel Scroll or some dice in case you want to really gun for a different spell and don't want him stopping it. I give it a 4 out of 5, and a recommendation to keep this spell if you roll it up. And remember, it's an Augment spell, no matter how much it seems like a Hex!

Spell #2: Blades of Putrefacation
An Augment spell that gives the targeted unit Poisoned attacks until the start of the caster's next magic phase. This spell has a range of 12" and a base casting value of 8+. In addition, if the targeted unit already has Poisoned attacks, it's attacks automatically wound on a to-hit roll of both 5 and 6. This spell is obviously very nice, because it can be combined with Miasama of Pestilance for a devastating one-two punch. Drop their Weapon Skill and Initiative and then make yourself automatically wound 1/3rd of the time you roll to-hit. I have seen a horde of Plaguebearers sandwiched between a unit of Blackguard and a unit of Cold One Knights, and with these two spells, it absolutely obliterated the Dark Elf units. I give it a 4 out of 5, with a recommendation to combo it with Miasama of Pestilance.

Spell #3: Curse of the Leper
This is one of those spells I really wish that in 9th edition we see more and more of. If targeted at a friendly unit, then this spell is an Augment. If it targets a foe, it is a Hex. It will respectively either increase or decrease the targeted unit's Toughness by D3 until the start of the caster's next magic phase. This spell has a range of 18" and a base casting value of 10+. It can be boosted to have an increased casting value of 13+, but it also increases the range of the spell to 36". This spell is really nice and very utilitarian. It's not as good as say some Shadow or  Death Hexes and Nurgle stuff is pretty tough all in all, so it may seem unnecessary at times. However, if you play a lot of stuff that hits hard or against a lot of artillery, then this spell has its uses. I give it a 3 out of 5, and a recommendation to swap for it more often then not. Again, it's not a bad spell, but it can feel very unwieldy at times.

Spell #4: Rancid Visitations
A Magic Missile spell that has a range of 18" and a casting value of 10+. It inflicts D6 Strength 5 hits, and in addition the targeted unit must then pass a Toughness test immediately suffers an additional D6 Strength 5 hits. This continues until a Toughness test is passed or the target is removed as a causality. This spell is the best way for you to avoid those annoying little pests like Skaven Slaves, Zombies, Skeleton Warriors, Skinks, etc. It's also a great way to clear chaff and thin down rank-and-file hordes of core infantry. If I have one complaint with this spell, it's the range of it. However, if it was any further, it probably would be the best Magic Missile spell in the game. I give it a 4 out 5 and a recommendation to jump up in joy should you roll for it.

Spell #5: Fleshy Abundance
Here we go, getting back to the bread and butter of Nurgle magic! This is an Augment spell that has a base casting value of 11+ and a range of 18". It grants the targeted unit 5+ Regeneration and should the unit already have Regeneration of any kind, it adds +1 to that save (maximum is a 2+). These effects last until the start of the caster's next magic phase. It can be boosted to effect all friendly characters within 18" for an increased casting value of 22+. This spell is kind of a double edged sword if you play Daemons. The problem with Daemons is that you already have a 5+ Ward Save universally. And given 8th edition rules, Regeneration and Ward Saves cannot stack as they once did. If you play Warriors of Chaos however, then this spell is freaking beautiful. Especially if you're that jackass who plays Throgg and his Troll Horde. Also, if you play with a lot of monsters, then this spell can really help you deal with any artillery that isn't Dwarf artillery. Good spell to have, I give it a 4 out of 5, but if you play Daemons, again keep in mind who's going to be the benefactor of this spell.

Spell #6: Plague Wind
I can just see those little Skaven fuckers squeaking copyright infringement over this one. It's a Magical Vortex and works like every other friggin Magical Vortex every put to words. Any model touched by the template must pass a Toughness test or suffer a wound with no armor saves allowed. It works in subsequent turns like Purple Sun. It has a base casting value of 15+ and can be boosted to use the large round template for a new casting value of 25+. I don't like it all that much, and it's kind of misplaced in a lore dominated by Hexes and Augments. The important thing to note is that is doesn't scatter farther when it's boosted, making it the second most accurate Vortex spell besides the Dark Magic spell Black Horror. I give it a 2 out of 5 though because I simply do not like Vortex spells all that much in general.

So that's the Lore of Nurgle, and it's arguably the best lore out of the three Chaos lores in general. It doesn't really have any power spells like the other two, but it's combination of spells and synergy gives it an advantage that the lores of Tzeentch and Slaanesh simply do not have. Without further ado, let's talk about strategy.

Daemons of Chaos: This lore is the best one you can take save perhaps Death and Shadow. In an all Nurgle list (aka; a competitive Daemons list) this is certainly a lore that you want to take into consideration. Death has it's range issues and Daemons really do not a lot of support, even Nurgle stuff that's tough as rocks is in serious need of support in terms of Weapon Skill and Initiative. Plus, it has Augments and Hexes which lore of Death does not. Bottom line, I highly suggest this lore because it is very useful for the Daemons and makes a brick of Plaguebearers the tar-pit unit from hell.

Warriors of Chaos: Since Lore of Beasts is not accessible to the WoC, then might I highly suggest taking this lore if you want to trick out your Chaos Warriors even more then a 4+ base armor save and a stat line that allows them to dickslap pretty much any other infantry, especially when marked to Nurgle. If you're more one for Augments then Magic Missiles or Direct Damage and/or you really have a hankering for taking one of their Signature Lores then this is certainly the lore to take. Plus, you can make your casters pretty much invincible with a successful casting phase.