Robot Mode: Mainframe sports a sort-of futuristic look that reminds me of early comic space robots, but is otherwise unremarkable. Like all Actionmasters he's quite posable.
Add-Ons / Partners: Mainframe used to come with Push-Button, a small transformable tank.
Missing Parts: Push-Button got lost long ago and nobody cared. Certainly not me. Mainframe also lost his handgun.
Remarks: Whoever had the idea to issue non-transformable Transformers? With the Transformers line in decline around 1990 Hasbro issued the Actionmasters, comprised of new and classic figures that couldn't transform. The idea didn't sell (big surprise!) and the decline of Transformers continued.