Immortals Set

The D&D Immortals Set was released in 1986, a year after the publication of the D&D Master Set, and serves as the cosmological capstone to the BECMI line.

D&D Immortals Set (1986).  Cover illustration by Larry Elmore.

The two-volume boxed set includes a 32-page "Players' Guide to Immortals" and a 64-page "Dungeon Master's Guide to Immortals" (52 pages, containing a 12-page "Reference Guide" insert in the middle of the book, removable by opening the staples).

Although material was included from "Eldritch Wizardry" (primarily the demons), together with inspiration from "Gods, Demi-Gods & Heroes", Frank Mentzer was credited with the sole byline.  Neither Gary Gygax nor Dave Arneson are mentioned.*

*likely related to Gygax's ouster from TSR in October, 1985

Editing was by Anne Gray McCready (previously Anne C. Gray, who also worked on the previous boxed sets in the BECMI line) and development was credited to Harold Johnson.

Interior illustrations were by Larry Elmore and Jeff Easley, continuing the look and feel.

Advertisement for the D&D Immortals Set, from Dragon magazine #114 (October, 1986)

The idea for an Immortals Set was originally hinted at in "A New Game With a Familiar Name" by Mentzer in Dragon #77 (September, 1983). 

At the highest levels of power, the characters may strive for the greatest of goals: immortality. Details and procedures will be provided, and the adventure does not stop even at that high point, for the Immortals have their own adventures and methods of progression.

Frank Mentzer, Dragon #77 (September, 1983)

Frank's ideas continued to evolve as he worked on the BECMI line, as evidenced by the need for corrections (see "Corrigenda" in the DM's Guide to Immortals (pg. 14) in which it's stated that some of the details given about Immortals in the D&D Master Set were incorrect and/or oversimplified).

While many consider the Immortals Rules as a kind of "sequel" to the D&D game (Frank has gone on record to state, with some justification, "my goldbox transcended D&D"), the material actually serves as the final endgame to the material presented in the D&D boxed sets.