The following comes with a "health warning" - I am still trying to make some of these strategies and tactics work in practice as I am quite often let down by bad dice - as some of you will know from first hand experience
On Eldar tactics as a whole, the concept behind the Eldar is that they are "Soap bubbles with sledgehammers" - brittle troops that can pack a big punch. They must use their mobility and cover to set up overwhelming assaults on their own terms while avoiding being shot or assaulted on the enemy's terms. (I presume that everyone has something like 30-40% of their battlefields covered in terrain - check out Chroma's battle reports to see what I mean). Their weak armour makes Eldar especially vulnerable to air assaults, so they usually need to ensure good air-cover of their own (Night Wings and Firestorms are both the best of their class in the game).
Eldar SR 4+ means that they can usually get the drop on IG, but need to be more cautious with Orks and Marines. Their Initiative of 2+ and especially the removal of Spirit Stones makes most Eldar formations very susceptible to BMs, so use cover and Marshall when a long way from the enemy. This also makes a Supreme Commander a "must" both to keep the army moving and to remove a BM from that Aspect Troop.
IMO Eldar generally need to keep an activation advantage over their opponents, so I try to get an average formation cost of around 250-300 points (10-12 formations in a 3000 point army). This allows the Eldar to try to move major formations later in the turn to places that cannot then be threatened by the opponent. ÂÂ
The Eldar player must try to capitalise on the Eldar strengths
- Hit-and-run (especially after an assault by moving to support another engagement or away from retaliation).
- The "extra" retain to hammer opposing forces
- The "Free" Avatar to initiate assaults with Commander etc
- The generally superior mobility (35cm Skimmer) capability to concentrate attacks on part of the enemy while avoiding contact elsewhere.
In general, the Eldar formations are quite weak individually, but their mobility also means they can spring co-ordinated attacks from long range. Their weakness also means that they generally operate best in a 'counter-punch' mode - reacting to opposing threats and to exploit exposed weaknesses. Eldar should really only attack when they can be sure both of winning and also of minimising potential retaliation. As a general rule this also means they need to try to concentrate on the flanks of an opposing army rather than on direct confrontation.
On the formations mentioned above:-
Fire PrismsFire Prisms should always double when firing, moving back out of range / behind cover after firing. Lance, skimmer and their long-range make them quite good first-strike anti-tank weapons with the potential to lay AA BMs, but they are notoriously brittle, so must be kept out-of sight as much as possible.
FalconsAs Rug says, Falcons have good firepower, but it is a little short-ranged compared with IG, so they must also double making best use of cover - but they do make excellent support formations with their 4+ FF. Try doubling them forward to fire on an assault target, and them using Guardians in Wave Serpents to make the assault. They also allow the deployment of Firestorms for the AA umbrella.
GuardiansWhat's not to like about these? Ok, they have no armour (so keep them in cover or vehicles). They are cheap at 150 points each, To get shooting, you can swap out some for Heavy Weapons, or buy some upgrades. The Wraith Guard and Wraith Lord are awesome upgrades and Guardians do get a lot of FF 4+ dice. The Farseer gives commander besides getting a good CC attack and 4+ armour & Inv, and also gets the Farsight rule and the ability to deploy the Avatar. Everyone should have at least two of these formations in a 3000 point army
EoV troupesBoth a strength and weakness on the Eldar army. DC3 makes them harder to surpress, so on a par with the Falcons and Prisms and 5+RA makes them much better armoured. Most work well in pairs, but they then become bullet magnets, so I generally only use singletons (which also keep up the activations).
- Scorpion - heavy duty firepower, it is good for long-range Anti-tank duties, and more effective as two or a pair.
- Cobra - a singlton is really good at frightning infantry formations, and two (or possibly a pair) can seriously hurt / destroy most titans. Their short-range fire-power means they must make maximum use of cover and double or march into position later in the turn - but are fearsome once they get there. Limited AA capability also helps provide some protection against air-assault.
- Void Spinner - one of the best artillery in the game that combines mobility with range and disrupt.
- Storm Serpent - Provides the Eldar with long-range assault capability in a reasonably rugged WE with adequate support and AT as its secondary role. They are automatic targets of choice because their destruction can severely restrict Eldar strategy, so you should always have a minimum of two, and preferably a Wraithgate as well. But when working in co-ordination with each other and other formations, they can deliver a massive, supported assault that can wreck a significant part of the enemy army.
Night SpinnersLike many other Eldar formations these come into their own when you have more than one formation. They are nortoriously brittle, so need to be "hidden", and at 90cm range indirect, they are amoung the shorter ranged artillery. However, their 35cm move means they can claim objectives in turn three and disrupt makes them quite potent - especially against infantry. So you need to deploy them behind (or even in) cover, and protect then against air-assault with good AA cover.
AspectsIMHO all aspects are costed about right with the possible exception of Warp Spiders (slightly too cheap) and Banshees (slightly too expensive). The point is that they are intentionally very good at one style of fighting, but otherwise mediocre. IMO most work well in combination with other Aspects, though Spiders and Hawks are best used alone.
- Shining Spears
Shining Spears with 2x Exarchs can make very fast, hard assaults out of the Webway at a slightly greater distance than other Aspects (35 cms vs 30cm to make use of their CC attack). However, I also like to use a pair of them to reduce the cost of Aspects in Wave Serpents by 50 points per pair, or the equivalent of adding a pair of Exarchs.
- Howling Banshees
IMHO the most problematic aspect, because of their weaker armour combined with CC assault. Put them in Wave Serpents to improve their survivability and assault range and combine with 2x Fire Dragon Exarchs which makes them quite potent - but really they only work well against weaker targets. (I used this combo to toast a Warhound with First Strike and then scoot back to safety). However they tend not to be used because there are better Aspects around.
- Striking Scorpions
First class assault troops with good armour and 2x attacks. The classic combo is with Dire Avengers to provide good assault and support capabilities. A really viable alternative is 3x SS, 3x DA with 2x Fire Dragon Exarchs for additional MW firepower, again in Wave Serpents for added resilience and mobility.