FACTION: SKAVENTHE BACKGROUNDThe Skaven clans were created long ago by dark, chaotic magic. These rat-men, with their obsession for collecting and using powerful wyrdstone rocks, are feared across the known world and far, far beyond. The Grey Seers and Warlords that lead Skaven armies run a great under-Empire - one that can burst forth with terrifying power.
The Skaven lands are spread out. Lustria is one theatre of war with obvious opportunities, and the World's Edge Mountains can also form an early base. Capturing human cities around their capital of Skavenblight can also help protect it - any action risks the wrath of other factions nearby, but the Skaven's ability to churn out large numbers of rats from early in the game will help in territorial siezures. The split territory can be an opportunity, but also a weakness.
Skaven lack discipline and power, but make up for it with numbers and a careless disregard for life that allows them to mount suicidal attacks and still have many, many troops in reserve. Spear-carrying ranks of clanrats are backed up by more powerful units such as Stormvermin or deadly Rat Ogres.
Coming from below, the bells toll to bring hordes of slavering rats pouring up into the lands or man, dwarf, elf, or lizard. Truly, the coming of the under-Empire will be a sign - if ever there was one - of the coming of the End Times.
IN CAMPAIGN
The Skaven are the archetype of an "early game" faction - their starting territories are spread out, but with good facilities for rapidly producing large field armies early on. Their four starting provinces are Mousillon, in the centre of Brettonia, Karak Varn, on the west side of the World's Edge mountains and just east of the Empire, Skavenblight in northern Tilea, and Quetza, an occupied Lizardman city al the way down in Lustria. Expanding quickly is vital. Besides Mousillon, all the starting provinces have nearby rebel settlements which you should aim to swamp with rats as quickly as possible. The reason for this is the Skaven unit roster. It has some effective units in - stormvermin are very tough, rat ogres are big and scary, giant rats useful for chasing down fleeing enemies, and warpfire throwers are excellent for killing enemy monsters. As a late game unit roster, though, it's vulnerable. The skaven don't have really effective counters to artillery and high-end cavalry beyond the basic principle of massive numerical advantage - which is a pretty good principle, but you need to have enough cities churning out rats for it to work.
The four starting locations each have their own quirks. Mousillon is the most vulnerable, and above easy difficulty setting it's tough to hold on to or expand from as those dreaded heavy cavalry will be running you down pretty quickly and all the neighbouring settlements are held by factions. Karak Varn is fairly safe, and has defensible mountain passes nearby; taking Karak Ungor or Mount Gunbad can be useful in giving you a base to attack the richer provinces of the Empire from the east. Your nearest opponents are actually the Vampire Counts of Sylvania; taking them on can be a good strategy, not least because as the owner of a horde of nervous rats the last thing you want to be facing is an equally large horde of scary undead who have the sort of morale levels that a Skaven commander can only dream of! Skavenblight is your capital; the nearby cities of Miragliano and Tobaro are well defended, but vital as they guard the entrances to Estalia, Tilea and the Empire, making them strategically vital. They're also quite wealthy areas, so Tilea and Estalia can be some of the best early pickings for Skaven expansion. Quetza is a very different story and a very different part of the world. It is in a good area for very rapid expansion, and Lustria can be a real Skaven stronghold; moving early is even more vital here than in the Old World, though, as higher end Lizardmen troops such as skink priests or the stegadon are excellent against massed infantry forces such as those the Skaven tend to field.
Skaven are, ultimately, one of WHTW's most horde-optimised forces in campaign, though this can be deceptive; to win, you need not only a talent for getting enough rats to the right places, but knowing when to use your few extremely powerful (but often fragile) attack units; the assassins and the warpfire throwers are key here in the later game. The other thing you need to get a feel for are your building trees. The clan system is all important for the skaven; Eshin provide the assassins, gutter runners and night runners, Skyre the jezzails and warpfire throwers, Pestilens the dreaded plague monks, Moulder the giant rats and rat ogres. These are done via "temples" - in other words, you can only pick one clan per settlement, so knowing which in order to get the troops you need where you need them is vital.
TROOPSTactically, the skaven are an infantry-only force that relies on horde tactics with a few hard-hitting missile and infantry units providing exceptional killing power. Being able to use foot troops to their best is therefore vital; skaven are, perhaps along with undead, one of WHTW's real "massed infantry" factions. Simply swamping an enemy with numbers is a valid tactic; it is certainly not all the skaven can do, however, and doing it effectively requires a great deal of skill.
The basic line infantry are the core of the skaven army: skavenslaves, clanrat spears & swords, and stormvermin. The slaves are your ultimate meat shield; unlikely to kill anything, but very cheap for absorbing enemy shooting or slowing down enemy infantry. The clanrats are a little more promising; they can hold a line without too much difficulty, and are only a little bit worse than basic-tier human infantry. Certainly they’ll get carved to bits by anything particularly tough or nasty though. The stormvermin are your general’s guard unit, and are rock solid. These guys should be the real anvils in your battle line, and are far tougher than your basic rats. Using a mix of all three units is vital; the lower levels can absorb charges and shooting so the higher can get in some actual kills.
Around your line infantry you have your specialists, from the different clans. Moulder we’ll talk about first; Rat Ogres are a really necessary part of your army. Scary, hit a lot harder than regular troops, and – don’t underestimate this – faster by half. Use this as counter-punching units and fast reserves for after your battle line is engaged, and let them loose on expensive enemy units. Getting them bogged down in cheap troops, particularly halberdiers or axemen, or letting enemy artillery pound them too much is a mistake though. The giant rats are perhaps less necessary, but very worth a look. For running down fleeing enemy troops they’re about the fastest thing you have, and they can really break up an advancing enemy formation as well.
Pestilens have just one unit, the plague monks. These are an additional form of line infantry, not quite up there with stormvermin for toughness but with the bonus of causing fear. They are also useful for their magical chant ability; use this to bolster key parts of your battle line and boost nearby troops. The Plague Monks are incredibly useful and versatile for boosting the key points in your infantry line, particularly against low-morale foes or where you absolutely need your clanrats to hold firm.
Skyre provide your jezzails and warpfire throwers. Both of these are literally crucial. Your jezzails are the only unit in your army with semi-decent range, and as such should be targeted at more heavily armoured enemies who your clan troops will struggle to pull down easily. They’re not so accurate as Thunderers or Hochland long riflemen, but certainly do more damage than regular Empire handgunners and armour piercing bullets are always nice. The warpfire throwers are more specialist, with shorter range but a huge attack. These are some of the best monster-killers and heavy enemy destroyers available to the Skaven – a barrage can knock out a large chunk of even a pretty heavy enemy infantry unit.
Finally, Eshin. They have three units – night runners, gutter runners, and of course assassins. The night runners are a cheap light infantry unit, roughly on a par with clanrats. The Gutter runners are much more useful – they have low defense but high attack and good hiding abilities, making them excellent sneaks and ambush troops as well as flankers. The assassins are the real jewel in the crown of the force, though. These guys have low armour but some of the highest melee attack values for an infantry unit in the game –they can be easily shot or destroyed on a charge if caught in the open, but they can also slice through even very powerful enemy forces with ease as long as they can sneak in and hit them when they are already engaged. These guys are most useful for taking out enemy generals and their bodyguards, or slicing through ogre-size units that the regular rats will have more difficulty with.
CoreSkavenslaves
Clanrat Swords & Spears
Stormvermin
Giant Rat Packs 
Night Runners
Jezzails
Special & RareGutter Runners 
Assassins
Warpfire Throwers
Rat Ogres
Plague Monks
