To spawn Vyzh`dra the Cursed:
Kill the seven Taskmasters (Kavamezh, Keuzozh, Mikazha, Revan`Kezh, Vezhkah, Zerumaz, and Zhe`Vozh), the two Rhozths (Ssrakezh and Ssravizh), and Warden Mekuzh.
Doing so spawns a glyph covered serpent. Kill this to spawn Vyzh`dra the Exiled. Kill him to spawn Vyzh`dra the Cursed.
Note: A rune covered serpent and Vyzh`dra the Banished will appear in the aforementioned mobs' places if they have been killed prior to an unsuccessful Vyzh`dra the Cursed attempt. The only difference is they will not drop loot.
Vyzh`dra the Cursed himself casts an AE Charm which can make this encounter interesting...