unique mobs?Follow

hello everyone:)
i have a little question about unik mobs :P
i know there is some elite... but i mean is there unik mobs outside instance, like leaping lizzy in FFXI ?
this one, krethis shadowspinner http://www.thottbot.com/?n=2142 looks like one...but what i really want to know is: is there a way to spawn them? like in FFXI kill the mobs of the same familly than the unik for spawn it within 2hours? or have they spawn time like in anarchy online of 18hours or 20mn ....?
or do they spawn randomly?
thx for all information u can bring in:) and osrry for my english i hope u ll all understand what i mean :P

well i ll try to explain better...
look at this mob http://wow.allakhazam.com/db/mob.html?wmob=462
it looks like an unusual one...not like a random mob...and what i would like to know is if u can make him pop by killing all the carrion bird around his spawn area? or does this Vultros spawn every hours or more? or is it a random time spawn?
hope its explane better than my other post
thx all :)

Named mobs are usually or always used in quests. They have a random spawn unless it is a quest that forces you to spawn it(usually with an item aquired from the quest giver)

There are some elite mobs that spawn randomly around the world, that aren't quest related in any way. They're just rare spawns.

There are also random named mobs with a silver dragon portrait that are also a rare spawn. They aren't quest related, but have a 100% chance to drop green item or better. If they don't drop a green item that means they're bugged. Sucks to kill a level 57 'half leet' that doesn't drop an item. :\