Have you ever stopped to wonder why Harlequins travel in packs? In the darkest nights, they remember they are not the apex predator of these twisted pathways...
Some say that of all the thousands upon thousands of Young Kings sacrificed to awaken the Avatar of the Bloody-Handed God...he is the only one to have been found alive. Perhaps this is true. Perhaps something altogether worse...
Our people must be strong to face that which is coming. The weak have no place by our side, lest they be the spear that wavers, the shield that drops, the flank that folds. - Message scrawled in blood, discovered atop the Laughing Mount
Remember the true nature of our Gods, cousin. The craftworlders may have cast him as their God of War, but first and foremost...Khaine is God of Murder.
This guy's another idea I had on the take of an eldar outcast. Basically, the idea behind all of my eldar projects is to take the INQ28 style approach to the eldar. One side of that is to have a really fine-grained look at each eldar faction, and creating a whole host of subfactions and individuals within them to make them feel every bit as varied and conflicting as the Imperials.
Another side is to expand the environments of Craftworlds and Commorragh and the Webway and such into living and breathing places within which people might want to set INQ28-style campaigns. You see that a little with the fluff of my Nomad Prince and the ruined city through which he's currently wandering (although I want to take it further). The idea that the webway isn't just a tunnel through which you walk and pop out of the other side, but a whole realm to be traversed and lived in consisting of the ruins of the various webway realms that were destroyed in the fall.
The last side is to fill said realm with monsters.
That's who this guy is. The Young King stalks the webway hunting eldar. As with all of my villainous characters, I adhere to the golden rule of 'no-one is the villain of their own story'. He truly believes he is murdering eldar for the good of the eldar. If you are weak enough for him to murder you, then you are not strong enough to face what is coming and will only prove a liability.
Note though that the only condition for victory against this character is 'survive', not necessarily to best him in combat. Running away is a perfectly viable tactic. If the eldar face up to the Rhana Dandra and lose, they will need the best cowards in the galaxy to flee and ensure the eldar survive.
The last thought on this guy is that both Cegorach and Ynnead have empowered champions to do their bidding. Khaine, although rather indisposed at present, would seek to do the same. The Young King is an instrument of Khaine's will, and exemplifies the logic behind the War God, Murderer of Eldar. Kill or be killed. Only the strong will survive.