This is a video, how we successfully down Lady Vashj with 4 man.

This will be more an interesting watch for those, who killed her in TBC. Do not expect perfect play. I am pretty confident, that this is also possible with 3 man, but then one has to get a lot more lucky with tainted spawns.
You'll see very little and dilettantish editing,
Song: Kojima Mayumi - unknown title (Ai no Poltergeist album)

You has the tainted core!