The death of Orcus info needed

[Alzrius]

Can you or someone remind me where Mystara's Orcus is described?

Your best bet is probably going to be Wrath of the Immortals, though there isn't much there, IIRC. There's also some information in the old Set 5: Immortal Rules and the adventure M2 Vengeance of Alphaks.

As a bit of trivia, M2 is the code also assigned to the adventure Maze of the Riddling Minotaur. The code for Vengeance of Alphaks, being a solo adventure, should have been MSOLO2. Thank you Acaeum!