This quest has been serverly nerfed, thus, fully doable with a reasonable PuG.
(Don't let the oldschooler's frighten you!).

About the quest, In the basement of scholomance (Room of Rattlegorge) there are alot of pretty nasty skeleton-like creatures - This room has to be cleared, once cleared the scryer has to be used on a pile a little further back in the room (from the entrance).
After one has used the scryer the group should quickly move into the south east corner (from the entrance) - doing so will allow you to have mana breaks from time to time.
This is where it becomes intresting (well, used to) because it activates an event, wave event, were waves of ghosts fly freely through the basement.
After each wave is killed, a new wave appears, eventually summoning Death Knight Darkreaver.

A good lineup includes a Warrior(tank), Priest(shackle), and random DPS (the less mana, the more effective).

- Merowlin

Before the event is triggered, the group will want to go to the corner you'll face by entering the basement and turning right 90 degrees.

There are four waves. After each wave, you fight a named mob called ""Aspect of [something]"".

Wave 1: As soon as the Divination Scryer is placed, 9 or so very slow moving mobs spawn. It is recommended that the shaman kite the slow movers around the room, making them even slower with earthbind totems. The shaman should be able to avoid taking damage the entire time. One of the other party memebers should start pulling each mob off of the shaman one by one and training it to the rest of the group, who should kill it.

Kill all 9, a named comes. Make sure that everyone is in the corner mentioned earlier when the named dies.

Wave 2: Mobs will spawn one at a time. Once you kill one, another will spawn.

Kill all 9-ish, another named appears. Again, make sure you're in the corner when he dies.

Wave 3: 3 linked groups of three spawn. It is recommended that you take the group out by the enterence first. If you have a warrior, have him hug the wall and charge one of the three in that group when they are furthest away grom the middle group. If he accidently pulls the middle group, let him die, res, and try again. If he succeeds, the rest of the part should hug the wall to the other side and take out the group of three. Afterwards, take out the middle group, then the far group.

Kill all three groups, a third named spawns. Again, make sure you're in the corner when he dies.

Wave 4: One mob spawns, then subsequent ones spawn on a timer. It is important to DPS each one as fast as possible, as these hit hard. You can make life easier by dropping a grounding totem, as that will absorb their hard-hitting range spell. If you have two shamans in the party, it makes it MUCH easier.

Kill all 9-ish, another named appears. Kill him, Death Knight Darkreaver spawns. Kill him for the win!

since nobody bothered to mention I should probably tell you that you should clear the entire room even at level 70 as the skeletons will aggro instantly and are quite strong

if you fail the quest you also need to reset the instance, abandon the quest and go and retake the quest.

Does NOT count for Loremaster of Kalimdor Achievement.