Wraithseer
The Wraithseer is an Eldar wraithbone construct in the same family as the Wraithlord, Wraithblade, Wraithknight, and Wraithguard in that they're powered by the dead.
However, whereas Wraithguards and Wraithblades house Aspect Warrior souls and Wraithlords house Exarch souls, who are then shepherded by a Spiritseer, the Wraithseer cuts out the middleman and puts in a Spiritseer's soul stone as the pilot, allowing them to exert greater control over his wraithbone shell and the shells of others. In a way, they resemble the Blood Angels' Librarian Dreadnoughts, except they're not quite as ridiculous a premise. However, they're just as grand a rarity, as the secrets behind making these psychic machines is lost to the general populace. Also, despite the badass practicality, these titans are used more as a last-ditch resort, more so than using Wraith-constructs normally entail.
On the field, it is a legendary thing to field if your opponent lets you field Forge World. It has both incredible support for other Wraith-units and for combat a Wraithseer is always equipped with a Wraithspear and Wraithshield, and may also arm themselves with a Bright Lance, Scatter Laser, Eldar Missile Launcher, Starcannon or D-Cannon.
Their psyker abilities are also quite potent, allowing them to assist friend and hamper foe. Wraithseers have been known to cloud their enemies' minds with the terror of death, enliven the spirit stones of ghost warriors around them to inspire fresh vigour, and alter fate to protect themselves and their charges.