Die Vecna Die!

Die Vecna Die! is an "Advanced Dungeons & Dragons "(AD&D 2nd edition) module released in 2000 by Wizards of the Coast, Inc.. The module is divided into three sections, each taking part in a different campaign setting: "Greyhawk", "Ravenloft", and "Planescape". It was one of the last official adventures released for the 2nd edition of "Dungeons & Dragons".
Plot summary.
This adventure, and Vecna's multiverse-shattering plan contained within it, have been used by some "D&D" fans as an in-game explanation of the differences between the 2nd and 3rd editions of "Dungeons & Dragons". The closing paragraph of the module reads as follows:
Publication history.
"Die Vecna Die!" was written by Bruce R. Cordell and Steve Miller, with cover art by Paul Bonner and interior art by Kevin McCann. It is a 160-page softcover book designed for four to six characters of levels 10 to 13.
Reception.
Shannon Appelcline comments that for the end of the "Advanced Dungeons & Dragons" line, Wizards produced "Die Vecna Die!" as "an original adventure that touched upon the oldest locales and the most ancient myths of the "D&D" game, while still presenting something entirely new. The result was […] an adventure that played two ancient artefacts – the Eye and Hand of Vecna – against the cambion demigod Iuz and which featured a trek through the campaign settings of Greyhawk, Ravenloft and Planescape. It was the final product published under the TSR brand, the final book for "AD&D" and truly the end of an era."
In 2013, Alex Lucard, for "Diehard GameFAN", wrote that ""Die Vecna, Die" is more of a campaign than a mere adventure, and it’s arguably the most ambitious thing ever put out for Second Edition AD&D. "Die Vecna, Die" is no mere adventure, but a massive undertaking for high level characters, seeing them go through not one, but THREE different campaign settings. [...] Players will encounter some of the most iconic and evil characters in all of "Dungeons & Dragons", and have to witness firsthand the end of the Second Edition Universe, and the beginning of Third Edition. [...] It’s a damn shame how overlooked and underrated "Die Vecna, Die" is, as it’s easily the best long campaign like adventure ever put out for Second Edition. It’s a massive undertaking akin to, say "Horror on the Orient Express" for "Call of Cthulhu", but much like that seminal work, "Die Vecna, Die" is worth it, especially if you are a fan of any or all of the campaign settings that you will work your way through here".