I enjoy using somewhat unorthodox strategies, and there are none more eccentric than harlequins. So, I began using Harlequins sometime in the months before 6th ed hit us (upside the head).
I hardly see them at tournaments, but they are such great units (in the right hands), and often very misunderstood. I assert that the clowns are in fact one of the most competitive units in the Eldar codex. I want to help other craftworlders (and commoragh denizens) understand how utterly efficacious their most underrated unit really is by providing a Harlequin Tactica.

DISCLAIMER: I usually win a lot of casual games doing this, but have not taken any tournaments with Clowns yet. Suffice it to say, this stuff works pretty well, and is more informational for newer Eldar players who haven't yet considered using harlies. Eldar Vets, please be gentle.

1. ALWAYS take the shadowseer. Harlequins are t3 with a 5+ invuln. Most other opponents with any level of experience will blast the clowns off the table in the first turn, even if you were fortunate enough steal the initiative. You might as well have banshees for the points you sunk into clowns without this single unique advantage. Don't worry about

, and yes it's cheaty-faced, but so is at least one thing in every other codex. The Shadowseer's veil of Tears makes them tough as space marines when they so much as stand in front of a bramble patch. This she-Space-Elf turns razor-wire into adamantium and bombed out crack houses become imperial bastions at her presence. With the shadowseer the clowns are tough as terminators for roughly the same points and in some cases, less. They move through cover so you can bounce from one terrain piece to the next. Shadowseers, never leave home without one.
2.The Troupe Master. Yes, a power weapon is only AP3, and sure you're paying 20 extra points for what amounts to a sergeant. However, you're average clown is leadership 9, and the gig isn't funny anymore when they run off the table or just barely die from pot smoking doom of malan'tai rolls(10.5 avg on
3d6). You can't give them a warlock (for
Ld re-rolls) and as much sense as it doesn't make (fluff-wise anyway), they're not fearless. He gets a
PW (good vs
MEQ). No, you can't model a power spear or axe for advantage, it's simply not an option for him and any tournament coordinator or judge is going to shut you down. Power-anything isn't worth it anyway, when he can take a "Kiss" like everyone else which replaces his
CCW for free, and might make better use of it with his extra attacks. The Troupe Master is not popular, but not useless either. I take him for the utility. Sometimes.
3. Death jester. Similar to the Troupe Master in the way he changes up the act, but his prop works differently than the rest of his other thespians. The DJ is only 10 points more and his bagpipes of doom are fairly useful for pinning squads that the clowns don't want to entertain up close, or for closing in on fleeing jump units for the final act. They still have to fail
Ld checks to get pinned, but now shooting casualties make checks happen anyway, and over-watch boosted the defensive ability of the DJ slightly. Remember he gives up his extra attack in order to carry around his pimp cannon (it's a glorified
SC), so he's only got 2, and 3 when charging. A very good option for them when you've got the points.
4. Fusion Pistols. Take them. You want fusion pistols. You like fusion pistols. Slay the warlord? Yes, Please. Nuke a tank from behind. Okay, but keep in mind how close you have to get, and that models are removed from the front from shooting, so if that's your plan with them don't get blasted on your way in (you'll need another high threat model). Regular clowns are always more expendable. Don't be afraid to draw threat with them away from your softer elements. Try to keep a farseer (or jetseer) nearby to keep up fortune if it looks like the opponent has a lot of gunfire headed their way. The other benefit of the pistol is that is looks crazy scary and draws a lot of attention. As soon as you tell the other guy it's a "melta" he's going to unload into them (to no avail) so as to protect his metal bawkses. Clowns just laugh that fire-power off. No joke.
5.
HQs. There are a lot of juicy options for
HQs in an Elfdar Warhost, and some things just work better with Clowns than others, but the whole is always greater than the sum of it's parts. These things are meant to work in tandem.
A jet-bike farseer works well, if you're willing to pay the points, and the clowns aren't cheap either (the other half of your army better be cheap). He can boost around the board and throw out psychic powers willy-nilly like free candy, and the jet-bike helps him keep up with the Harlies, and still do other stuff. Always a solid choice. Always competitive.
Karandras has move through cover and stealth and he synchronizes nicely with the clowns and can bust open those high toughness
MCs with his 'zillion S8 powerfist attacks and his awesome weapon-skill. He doesn't have hit and run, but could cut them out of combats even they don't want to be in. He is expensive though. He's also
LD 10 and I7, so he's definiely your opening act in that group. Note that
HQs in that squad can take and make challenges, which helps a lot.
The Avatard is always solid, but take a farseer too. He's simply too much model to leave un-fortuned. It's an expensive setup, but his fearless bubble can help the Clowns ovecome that one glaring insufficiency. He can ignore terrain as
MCs do, but he's still slower than dial up. Use him as a distraction/support for them, if you like this setup. Wraithlords have good synergy in this build as well, becasue you have a lot of hardened targets that punch everything in the jeans in CQC.
The Autarch is pretty good, but doesn't have rending or any of their other toys. Sure, he can join them and with wings or a jump generator (I wouldn't advise this without a spider retinue) he can keep up. He could also do for the squad what the troupe master does, but takes an
HQ slot from our oh so precious farseers, and he's kinda point-expensive like money. With the right gear, he's not half bad. His
BS is like 7 (He [almost] never misses) and he can take a reaper launcher or fusion gun (melta). He's a useful option, but you need to plan him around the squads weaknesses.
Last but certainly not least is Eldrad "McCheatytrollface" Ulthran. 4 rolls on the Divination table, or Telepathy (some of which I don't find to be terribly useful). He can also take the (better) codex powers too . Invisibility for Clowns is just downright goofy (and a bit redundant, but could let you skimp on the shadowseer).
WS 1 for guys that get charged and no counter attack. This lets you play jokes on big mobs of stuff that can't hit you, and don't get their counter attack. Perfect timing could be hilarious for the DJ. Mental Fortitude could let you run them cheaper (no need for a Troupe Master), and both Terrify and Misfortune each could be pretty devastating(I don't think you can get them together). I don't need to mention Fortune, for the billionth time. It's pure gold.
Last and least of all, you CAN put them in a Wave Serpent (for those of you who give a

about those overpriced terrain pieces). Doing this is pointless, as they can move through cover and are tougher outside the transport, which could blow up and force invuln saves.
DE have assault transports, and the
HQs that allow for combat drugs on their own squad could be useful, but I'm inexperience with
DE, and they seem to only take wytches instead.
DE players, let me know if you come up with your own way of using harlequins to any effect in your army. I might take some
DE allies just to try it out.
Also, SUPPORT YOUR CLOWNS!! They aren't running arnound doing
CS GOTO spess muhreen stuff. They need help. I like to use Support weapons, because of how tough they got and utterly dirt cheap they are. They shoot everybody from the word go (except the poor D-cannon), and won't go down from stray bolter fire. I avoid mech (Vehicle wrecksidents are free points for my foe), and
WLs are nice, but I'm careful with them (
MC corpses are free points too). Ranger Pathfinders are perfect support for clowns, and have a lot of the same gimmicks they do(rending/ fleet/ move through cover/ pinning).