The Black Knight's Fall

It appears that this quest is bugged in 6.0

I tried multiple times to do this, but right after Black Knight knocked me off my warhorse he evaded and despawned.

Here's how to complete the quest atm:
1. Equip your lance and go get yourself a Stabled Argent Warhorse. (Located close to the flightmaster)
2. Go to Squire Cavin and ask him to summon the Black Knight. (Squire Cavin is the little orc boy standing at the side of the Ring of the Champions, little bit further east from flightmaster)
3. Wait for the Black Knight to run to the middle of the Ring and manually dismount from your argent warhorse.
4. Nuke Black Knight down without using the skills of Stabled Argent Warhorse.

EDIT: Did this quest on alt and Black knight evaded after I manually dismounted. Tried it again and dismounted a bit earlier and got the quest done. So it would seem that you must manually dismount after you see black knight, but before the fight actually starts.

Sadly, the Black Knight will likely be your least challenging opponent in the Argent Tournament. However, it does have a gotcha that may cause you problems. The fight is in two phases. Equip your lance, jump on the [npc=33870], and then talk to [npc=33522]. He'll call the knight out for you and you'll fight him on his gryphon using standard jousting tactics. When he's low on health, he will dismount and call you out for hand to hand contact. Do nothing to dismount yourself. When you see him dismount, that is not your cue to unequip your lance or get off your own mount. The game will do that for you and if you try to do it yourself the black knight will probably evade and despawn. While he's buffing himself you will have time to equip your normal weapons. Then just fight him as you would any other non-elite mob.

Edit: Apparently it's possible to kill him while he's still on his gryphon. I personally witnessed this happen once and have heard a couple other reports of the same behavior. Normally he will jump off and face you in hand-to-hand combat, however.

Note that you must use the "Stabled Argent Warhorse" to finish this. I tried four times riding my Warstrider and the game would not auto-dismount me after the Black Knight did. If I dismounted manually he would evade and then despawn.

Edit: The above problem has apparently been fixed in 3.1.1 and you can't summon unless you are riding the Argent Warhorse.

Other than this it's probably the easiest fight ever. The Black Knight puts up no defenses. Just get yours up to three, Charge him, hit him with your melee attack, and when he moves away to charge you, Charge him first and repeat.