Short answers, pulled from the story.
The Dungeons & Dragons Companion Set is an expansion boxed set for the Dungeons & Dragons fantasy role-playing game, first published by TSR in 1984. It was written by Frank Mentzer and supports character levels 15 through 25, covering advanced play including stronghold management and large-scale warfare.
Frank Mentzer wrote the Companion Rules set. It features art by Larry Elmore and Jeff Easley, and the two booklets inside were edited by Anne Gray.
The Companion Set covers character levels 15 through 25. It was the third in a five-part series of boxed sets that collectively spanned from beginning characters up through Immortals who had transcended the level system entirely.
The War Machine is a rules system designed by Douglas Niles and Gary Spiegel, included in the Dungeon Master's Companion, for handling large-scale battles. It was intended for warfare that serves as campaign background rather than the primary focus of play.
Reviews were mixed. In issue 31 of Abyss, Dave Nalle called it a hodgepodge and criticized the stronghold rules as confused and misleading. In issue 61 of White Dwarf (January 1985), Megan C. Robertson gave it a rating of 7 out of 10, finding it offered useful ideas for characters beyond retirement age.
TSR published the 10th Anniversary Dungeons & Dragons Collector's Set in 1984, bundling rulebooks from the Basic, Expert, and Companion sets with modules AC2, AC3, B1, B2, and M1 (Blizzard Pass), plus dice and character record sheets. Only 1,000 copies were produced, sold by mail and at GenCon 17.