Wraithknight
The Wraithknight is a massive Wraithbone construct, towering even over the tall Wraithguard and massive Wraithlord design to harvest new soul stones from Crone Worlds. They can be armed with a pair of massive fuck-off Wraithcannons, a Suncannon or a Scattershield Duel Disk and a huge Ghost Glaive.
They are for the Eldar what the XV-104 Riptide and Dreadknight are to the Tau and Grey Knights, except less stupid in the case of the latter. It is an enormous model and a lethal one, making it a massive fire magnet in a more literal way than usual. While it's WS and BS are kind of meh (both 4), it's a Jump Monstrous Creature with S 10 and 5 attacks and I 5. It's impressive in defence but not too much: T8, 6 wounds and 3+ armour; also the option of a 5++ blinding anyone at 6" each time it saves this way. Cool, but sort of disappointing. Deepstrike it for that O.O look on the other guys face.
Like other wraithbone constructs, Wraithknights are animated by souls of dead Eldar. Wraithknights are special because they also have pilots; in particular, the pilot must be the twin of the soul animating the machine. It seems that the designers must have been watching Evangelion or Pacific Rim the night before designing the Wraithknight.
Wraithknights like to be fortuned to forever laugh at all small arms fire and turn a one in three chance to successfully invulnerable save to a one in half chance, concealed, and renewed, but sadly cannot have their armor saves enhanced. Plonk one on a skyshield and place fortune on it to sneer at the very concept of dying. Don't forget that Forewarning and potentially Sanctuary are options, too.
As of the Codex Eldar: Craftworlds update, Wraithknights are now 295 Jump Gargantuan Creatures (cue outrage everyone jesus christ GW), and the Wraithcannon and Ghostglaive are now Strength D. This is in contrast to Imperial Knights which cost 370 or 375 points a model and have only one Strength D weapon (the Reaper Chainsword). Eldar players celebrated, while everyone else is wondering what the hell GeeDubs was smoking to think that buffing an already overpowered unit further still could possibly be a good idea. On the bright side, this thing is now LoW, so in a Combined Arms Detachment you get a maximum of 1 in your list, and in the Craftworld Warhost detachment, you can have up to 12 for each Guardian Battlehost, one of which costs about 500 points base. JESUS. MOTHER. FUCK. However, it's not a merciful note since literally this is now the rape machine to end all rape machines.
Note that while the new WK is extremely tough, each army usually has at least one way of beating it:
IG/AM: Lascannon spam out the ass SM/DA/Cult Mechanicus: Grav Spam out the ass Daemons: Daemon Prince of Nurgle with Balesword and either fleshbane reward or iron arm Khorne Daemonkin: D-thirster Eldar: you already have a WK D-eldar: ally in a WK Tau: Railgun spam out the ass Tyranids: 5 Flying Hive Tyrants