Phantom Battle Titan
The Phantom Titan is the largest Eldar Titan (If you discount on whether a Warlock Titan is a sub-category of a Phantom Titan the same way as how Emperor Titans are split between Imperator or Warmonger) known to the Imperium. Similar to its smaller cousin, the Phantom while a bit slower is still much faster than the Titans of other races, keeping in the theme of Eldar glass cannons.
These Phantom Titans are often considered as the pinnacle of Eldar land vehicles (Again, arguments flare up on whether a Warlock Titan should be more technologically sophisticated). Unlike the Imperium's Plasma Fusion Cores that powers up their Titan, the Eldar instead uses a specially constructed Wraithbone core which is some kind of wonky Eldar physics that allows the souls of a dead Eldar to move freely throughout the machine, which in turn gives the Phantom Titan powers like those of a Wraithguard/Wraithlord but unlike the smaller walkers, this Titan merges the dead Elfdar with that of its living crew; helping them guide them like a over glorified GPS.
Some Phantom Titans are driven by a single Steersman while others are guided by twins or triplets (Guess it is going to get a bit cramped up there). They are usually situated in the head cockpit which gives them a view 25 meters above the ground.
The Phantom's primary arm mounts can be fitted with twin Phantom Titan Pulsars, Distortion Cannons or a special Power Glaive known as the Ashuna-Valcry'le.
Secondary weapons mounted in its shoulders include Phantom Missile Launchers and either a Pulse Laser or Titan-grade Starcannon.
It is also protected by a Titan-grade Holo-Field projected by the large rear fins. Meaning that not only does this thing rape vehicles on the battlefield, but it is also going to be a bitch to hit with anti-titan weaponry (How the hell can you miss a 25+meter tall walker!? Holofields are not an excuse!).