Stranger Stalker is a triggered event that will occur when you proceed toward the General's room. You will see a triggered zone message, "You hear a strange slithering sound."
The Strange Stalker will then spawn on your raid the next time you start an encounter. You want the Stalker to spawn on you while you pull a Patroller, a trash mob. It would be a much harder fight if it happened to be a named.
Some guilds choose to have it spawn on the last trash mob in the zone, some choose it to be the first. Either way you decide to do it, you need to tank both mobs at the same time. You can not kill the trash mob first. If you kill the trash mob first the Stalker will wipe your raid. He goes Berserk.
Where you pull him is up to your guild. Many guilds pet pull the patroller because the stalker will spawn on your raid. Stalker does AOE just as he Spawns so if your guild isnt quite as geared up yet you might want to blade dance just before the pet aggro's the trash mob.
Patroller's do memory wipe so if you can put two tank classes on this guy to help from a someone else in your raid dying.
Stalker has 3 abilities to watch out for for. He has two Noxious AE's and One Curse that hits 2 people at a time.
The AOE's just need to be cured ASAP. If the first is not cured and the second one hits, your raid will go boom. Much like Venril Sathir if your raid has fought him.
The second is a Curse called Vortex of Venom. You have roughly 10 seconds to cure this curse off of 2 people in the raid, otherwise you go boom again. Setup your Cure Curse rotations and you will be fine.
Burn the stalker, then the Patroller add and congrats on your loot.