Die Vecna Die! (2000)

From the back cover:

"The End of the World Is at Hand

A hideous death cult has seized control of an ancient artifact-monument known as Tovag Baragu. The power behind the cult is the Old One himself, Iuz the Evil, demonic master of an empire. He's on an all-or-nothing quest for supremacy over the world - and the heavens beyond.

To stop him, heroes must face horrors never dreamed of, journeying to a shadowed city where Death rules and the living cower. Here, Iuz will achieve his mad dream by destroying imprisoned master of that alien citadel - Vecna, the mightiest lich, an immortal demigod.

Two items exist with the power to stop Iuz - the Eye amd the Hand of Vecna - but using them carries fantastic risks. Not even the gods know what will be unleashed when these items are fully activated.

Die Vecna Die! takes the heroes from the GREYHAWK campaign to the demiplane of RAVENLOFT and then to the PLANESCAPE city of Sigil. However, none of the material from those settings is required for play."