In 4th edition the Eldar were one of the most powerful armies.
However, in 5th edition they are somewhat weaker.
One reason for this is that 40k is now more focused on troop choices, in which the Eldar lag behind the Orks, Space Marines, and Imperial Guard.
Also certain key units such as the Falcon anti-grav tank and Vibro Cannons have been made less powerful.
In previous editions the Eldar were substantially more mobile than other armies.
Now, they have lost this advantage as everyone can run.
Thus they are now just a plain old elite army like the Space Marines, with lower toughness and armor.
This being said, some of their elite forces, such as the Avatar and the Dark Reapers, are really good.
Overview of the Eldar Force
The Avatar is best used in close combat.
Being a monstrous creature, the enemy squad members will strike before him.
Although this is a big disadvantage, his high weapon skill makes it difficult to land blows against him, and his high toughness and armor help protect him from wounds.
When the Avatar strikes back he is likely to cause significant casualties, because he has plenty of high strength attacks that ignore armor saves.
His good defensive skills combined with his offensive capabilities make it likely that he will win combat handily.
It is likely that he will run down the remaining members of the opposing squad as he has a very high initiative.
He is just as deadly fighting vehicles, as he rolls an extra die for armor penetration.
In addition to his skills in melee, the Avatar has a short ranged melta attack from his sword, The Wailing Doom.
This is strong enough to instantly kill most troops and thus is very useful against terminators.
Better still, it is an assault weapon, so he can use it and still charge into combat.
It is also equally effective at penetrating the armor of a tank.
It benefits from being AP 1, so there is a greater chance that it will destroy the vehicle.
There is more to the Avatar than killing power.
He is an inspiring leader which helps keep your troops in line.
This is particularly important if you are trying to hold an objective, or if you are trying to tie up an enemy squad in hand to hand combat with regular troops.
For example, a lowly Guardian squad defending an objective will not flee if it takes heavy casualties from shooting.
A large Guardian squad can potentially hold up an enemy unit in hand to hand combat for several turns even if they lose the fight, as they will not flee.
In 5th Edition The Avatar now benefits from the Run special rule which helps get him into combat faster.
This is very important as he is likely to be shot with everything that your opponent can throw his way.
This brings us to the subject of the Avatar's defences.
He has a high toughness, but not high enough to ignore lasgun fire.
Thus if he is shot enough, he will be wounded.
In addition to his high toughness, the Avatar has a molten body.
This allows him to ignore flaming and melta attacks.
This is very useful, as both of these weapons are quite prevalent.
He has a good armor save, as well as a better than average ward save.
He also has a decent number of wounds, so a lucky shot or two will not take him down.
You can expect it to take 144 lasgun shots at ballistic skill 3 to kill an Avatar.
It would take about 109 bolter shots at ballistic skill 4 to bring him down.
The Avatar is much less expensive than Chaos Greater Demons, and a bargain for his points cost.
He is a good addition to most Eldar forces.
The Farseer has incredible psyker powers and his high leadership gives him a good chance of using them.
Many people build armies around such powers as rerolling wounds and rerolling armor saves.
For example, a squad of Wraithguard with rerolled armor saves is very resiliant, and Pathfinders that reroll wounds are very deadly indeed.
Mind War is another potent power which can be used to destroy the mind of enemy heroes.
In addition to his offensive powers, the Runes of Warding are the bane of enemy psykers, making it quite risky to use their powers at all.
Some people mount Farseers on Jetbikes to make them more mobile and give them a better armor save.
Most people take Warlocks as a retinue for the Farseer.
This is known as a Seer Council.
They are most effective if mounted on jetbikes, but can also run around on foot.
One advantage of taking a Seer Council is that they count as a single HQ choice.
Since they have such good saves it is very difficult to kill them, thus denying your opponent a kill point.
Warlocks are also used to assist Wraithguard and Wraithlords.
They are also good close combat troops.
Like Farseers, Warlocks also have psyker powers.
However, their powers are much weaker.
One of the popular powers, destructor, is a template attack that roasts most regular troops.
Anoter power increases their squad's initiative and weapon skill, which complements their hand to hand prowess.
Eldrad is the Eldar's most powerful playable psyker.
However, he is very expensive.
For this cost he has higher toughness, a better invulnerable save, and a staff that ignores armor saves.
This makes him substantially more dangerous in hand to hand combat than a regular Farseer.
Further, he knows all of the psyker powers, and can use more psyker powers than other Farseers.
Lastly, he allows you to reposition some of your troops after your opponent has set up.
Overall, he is a very potent character.
Most people choose Autarchs because of their ability to help troops come in from reserve.
For this reason they are usually taken in pairs, so that you are essentially assured that your units arrive.
Autarchs can be outfited in a similar fashion to almost any Eldar unit.
This makes them ideal leaders for squads.
They will almost invariably be given a power weapon and mandiblasters.
Although on the surface this makes them look very effective at close combat, they suffer from low strength and have difficulty wounding enemy characters.
Further, they have low toughness and are likely to be cut down by regular attacks.
So, you have to use them with care.
They can also function as an a disposable harrassment unit.
In this capacity they are usuaully armed with a reaper launcher or mounted on a Jetbike.
If the enemy ignores them, then they can snipe away and contest objectives.
If your opponent devotes enough firepower to kill them, they waste most of their shots and your other troops are not being killed.
Yriel is a legendary Autarch.
It is natural to compare him to the Avatar, as they are both very good in hand to hand combat.
They cost the same number of points and have the same armor and invulnerable saves.
Yriel has lower toughness and fewer wounds.
His upsides are that he does not strike last, is fleet, and can join a unit, thus shielding him from most shooting attacks.
For the latter reason alone, I prefer him to the Avatar, as you can't kill a unit if you are dead.
He also has a special power that can be used once per game that can kill hordes of troops in close combat.
He can also take out vehicles if the need arises.
If you are considering taking a Pheonix Lord, first consider taking Yriel as he is less expensive.
The Dire Avenger Phoenix Lord is very expensive.
However, he is the only Phoenix Lord to have an invulnerable save, and can't be insta killed.
Further he can dish it out in ranged and hand to hand combat.
So if you need to punch through infantry then you may consider using him.
Jain Zar is the least expensive Pheonix Lord, and in my opinion one of the best.
As lord of the Howling Banshees you expect her to be a beast in hand to hand combat.
In this regard she does not dissapoint.
She also has several ranged attacks with a power weapon.
Simply put, she is a Space Marine's worst nightmare.
The Striking Scorpion Phoenix Lord has a ton of attacks in close combat.
However, we are currently awaiting errata to see if he can use these attacks with his claw.
He can also sneak up on the opposing force, so he can get into the fray quickly.
The Dark Reaper Phoenix Lord looks so cool.
Sadly his weapon just does not have the killing power that you expect from a Dark Reaper.
It is almost pointless to use crackshot with him as his weapon does not have a good AP value.
On the up side he can kill plenty of guardsmen, and is also decent in hand to hand combat.
Fuegan is quite powerful in hand to hand combat, as well as at medium range.
If you want to kill a vehicle and then massacre the troops inside, then he is a good choice.
The Swooping Hawk Phoenix Lord is a jack of all trades.
He can shoot foot troops, bomb massed infantry, kill vehicles, and assault in hand to hand combat.
However, he does not do any one of these things as well as other characters.
If you have the points to spare and want some flexability you could try him.
As you can see the Eldar have many command choices.
If you want to bring stuff in from reserve nothing beats a pair of Autarchs.
Another option is to take some Farseers and max out on psyker powers.
A third possibility is to pick some hand to hand gods like the Avatar, Yriel, and Jain Zar.
Dire Avengers are good troops.
On the surface they do not seem to stack up against Space Marines, as they do not have the Marine's range, strength, toughness, or armor save.
However, they are somewhat less expensive.
Dire Avengers' Shuriken Catapults do not have the range of bolters.
However, they can put out more firepower at a slightly shorter distance and are assault weapons.
The standard way to play Dire Avengers is to mount them in a Wave Serpent, drop several squads near an enemy unit, Blade Storm, and shoot them to bits with overwhelming firepower.
They can also be played more defensively, by taking advantage of their range, creating crossfire between several units of Dire Avengers.
In general they should be kept more than 12" away from enemy units, so as to avoid assaults.
The exception to this is if you achieve substantial numerical superiority you can move in, shoot, and then assault.
Dire Avengers just can't match up in a firefight against Tau Fire Warriors and certain other very shooty troops.
Their guns don't have the range, or the strength.
Fortunately they are more mobile and have a higher ballistic skill.
The best thing is to close quickly and assault.
Guardians are somewhat difficult to field effectively.
Their long range weapons are good, however only one such weapon can be taken per squad.
Their other shooting attacks have a short range and are only good for a turn before the enemy charges into combat (and slaughters the Guardians).
One option is to take a 20 man squad and manuver them into a position so that they can shoot.
Such positions are usually close to centrally placed objectives.
The second option is to take a 12 man squad and mount them in a Wave Serpent.
Drive them up, hop them out, and blast the enemy just like Dire Avengers.
They are particularly effective when guided by a Farseer.
Storm Guardians fair somewhat better in close combat, but usually lose combat because of casualties.
They can also take a flamer and melta weapon.
They are best used in large squads.
With all of this being said I prefer to take a regular ten man squad with a scatter laser.
Sit them in cover somewhere behind your lines and shoot away.
Guardian Jetbikes are very much like light cavalry.
They don't hit that hard, but are fast.
Pop in and out pestering your opponent.
You need to be careful with them as they are somewhat expensive.
They are good at racing in and capturing objectives late in the game.
Pathfinders are great but expensive.
They are most effective against expensive enemy troops and monstrous creatures, as they have a tendency to get swarmed by cheap troops.
Use them with Farseers to reroll cover saves and wounds.
When they are not shooting, they are great at running through cover to claim objectives.
They are more resiliant than most Eldar units thanks to their superb cover save.
However, their big downfall is the prevalence of weapons that ignore cover saves.
I like to use 6 man squads, as they are still reasonably inexpensive, but are difficult to kill unless they are assaulted..
The elite choices are where the Eldar Codex really shines.
Wraithguard have superguns.
They are also tough and have good armor.
On the downside they are quite expensive.
They can be taken down in close combat and their guns only work at close range.
In many instances the Fire Dragons can serve a similar role for about half the points cost.
Fire Dragons roast armored targets and heavy infantry.
Put them in a Wave Serpent.
Drive them up, hop them out and shoot away.
A 5 man sacrificial unit is very effective.
Striking Scorpions are very much like Space Marine close combat troops.
They have tons of attacks which helps them cut down opponents like Orks.
Their armor allows them to take some fire.
Their downside is that they do not have fleet like most other Eldar units.
This restricts their assault range.
An exarch with a power claw is essential.
I take them in units of 10.
The Howling Banshees are good at cutting down heavily armored infantry.
The only trick is getting them into combat without being shot to bits.
They are even more deadly when paired with a Farseer so that you can reroll wounds.
Like Striking Scorpions, I take units of 10.
Harlequins are powerful close combat troops.
They are deadlier than the Howling Banshees, but somewhat more expensive.
Through the use of the Shadowseer and their movement rules you can generally get them into combat unscathed.
However, they are quite fragile and liable to get cut down if you do not finish off your opponent first.
They are very effective counter assault troops, as your opponent cannot attack them in that instance.
As with the other close combat troops I take units of 10.
Shining Spears are great for assaulting heavily armored foot troops.
They speed up, shoot, and then assault.
Their downfall is that they are expensive and lack grenades, so they strike last if they assault into cover.
Make sure that you accompany them with a Farseer so that they can reroll their saves.
Warp Spiders are good at attacking lightly armored troops.
They also have the benefit of being well armored.
However, they are very expensive.
They are best used by jumping within 12" shooting, and then jumping away.
This helps keep them out of rapid fire range.
The Swooping Hawks are expensive.
They can be used to hunt vehicles, or to harass lightly armored foot troops.
Dark Reapers kill armored infantry.
Take a squad of three with an exarch with crackshot.
They can thin out such targets as Space Marine Devastator Squads, and Tau Pathfinders.
The D Cannon provides a good combination of anti infantry and anti vehicle fire at the expense of range and accuracy.
The Vibro Cannon is less powerful in 5th edition than in 4th, but is still a good choice as it can disable a vehicle or tie up a squad of troops.
The Shadow Weaver is much less expensive than the other support weapons.
However, it is only good at killing foot troops.
Wraithlords can now run.
Tool one up for close combat and run on in.
Unlike other dreadnaughts, Wraithlords have a toughness rather than an armor value.
This is a real blessing, as most regular weapons cannot wound a dreadnaught.
If you can take out your opponent's heavy weapons, the Wraithlords can run wild.
They are best fielded in pairs or trios.
The Falcon now functions as it was intended, as a compromise between the Wave Serpent and the Fire Prism.
It can carry some troops, and can also take some big guns.
Two or three Fire Prisms can combine their beams to great effect.
This works well to take out masses of heavily armored foot troops.
They are also a moderately expensive but effective means of anti vehicle fire.
Given that the game is now focused so much on troops, it is very important to be able to kill them effectively.
There are basically two types of troops, armored ones, and unarmored ones.
It is not so critically important to crack through enemy armor, as most troops will have cover saves anyway.
Thus, simply dealing large numbers of wounds will take down heavily armored troops and hordes alike.
Point for point, no other troop in the Eldar army puts out more wounds than Guardians.
Dire Avengers come in a close second, followed by Warp Spiders.
Thus these troops should form the core of your army.
One weakness of all of these troops is hand to hand combat.
You can back them up with survivable squads like Striking Scorpions or Warlocks, or death dealers like Howling Banshees and Harlequins.
In addition to troops you need to be able to kill enemy tanks and big scary creatures.
D Cannons are good at killing tanks as well as troops.
However, they have a short range.
A squad of Fire Dragons in a Wave Serpent or Falcon is another great way of destroying tanks.