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 Wrath-constructs normally entail.
On the field, it is a legendary thing to field if your opponent lets you field Forge World, although it can't be used as a lone HQ; it has to be coupled with someone else, presumably a Spiritseer. It has both incredible support for other Wraith-units and some incredible weapons like the D-cannon and the Brightlance to use.