From the video description:

Originally riffed for an MST3K CD-ROM game but deleted and lost forever: Frank & Trace take on What's it to You? AKA the Mylar short!

Come learn about the roughly 9000 uses for Mylar described in this video and maybe have a few laughs along the way with the classic Mystery Science Theater Mads!

Chapters:
0:00 DVD Menu
0:38 Joel's Introduction
5:52 110 Robot Holocaust
1:43:02 Life After MST3K: J. Elvis Weinstein

Originally available on MST3K Collection XXVI from Shout! Factory. Now uploaded to YouTube on the official MST3K channel.

DVD Extra from MST3K Volume XXXIX.

From Experiment 810: The Giant Spider Invasion.

Rebane is an interesting guy: owner of the "first full-time feature film studio in the Midwest." A Wisconsin legend!

From Experiment 813 Jack Frost.

There's no description to speak of; I think these are unused bits or outtakes from the Film Crew series Mike, Kevin and Bill did after MST3K.

From the description:

Originally aired on August 15, 1997, as part of the Sci-Fi Channel’s programming, The Making of Mystery Science Theater 3000 is a 23-minute behind-the-scenes special that offers fans an in-depth look at the show’s production during its eighth season.

This special delves into the show’s history, from its beginnings on KTMA to its transition to the Sci-Fi Channel, highlighting key changes such as Joel Hodgson’s departure and Mike Nelson’s takeover as host. Viewers are treated to insights into the writing process, set design, puppet construction, and the filming of both theater and host segments.

Interspersed with humorous interludes featuring Mike and the Bots riffing on behind-the-scenes footage, the special provides a comprehensive look at the creative efforts behind MST3K’s unique blend of comedy and science fiction.

This special was later included as a bonus feature in Mystery Science Theater 3000: Volume XXII DVD collection.

That one movie with the Paper Chase guy! DVD extra from Experiment 501 Warrior of the Lost World.

An interview with Don Sullivan, who played the "wayward son" of a movie star in The Rebel Set, and Chase Winston in The Gian Gila monster.

Description:

Darkstar: Robots Don’t Need SAG Cards is a 17-minute featurette included in Mystery Science Theater 3000: Volume XXIII. This documentary delves into the making of Darkstar: The Interactive Movie, a science fiction adventure game developed over a decade by J. Allen Williams.

The game features several MST3K alumni, including Joel Hodgson, Trace Beaulieu, and Frank Conniff, in dramatic roles, marking a unique collaboration between the show’s cast and the gaming world.

From the description:

Much Ado About Nanites is a brief yet delightful featurette that delves into the quirky world of the Nanites—those microscopic, self-replicating bots introduced in Season 8 of MST3K. This segment offers a behind-the-scenes look at how these tiny characters were brought to life, combining episode clips with insights into their creation and role aboard the Satellite of Love

Star of "Mitchell" and "Final Justice."

RIP, big guy.

From the description:

This 9-minute featurette, produced by Ballyhoo Motion Pictures, offers an insightful look into the 1967 biker film Wild Rebels, famously riffed in Mystery Science Theater 3000 Episode 207. Featuring interviews with director William Grefé, lead actor Steve Alaimo, and film historian Chris Poggiali, the documentary delves into the film’s production, its place in 1960s exploitation cinema, and its enduring cult legacy.

Originally included in The Mystery Science Theater 3000 Collection: Volume IX, this behind-the-scenes look is now available on the official MST3K channel.

From: Experiment 208 Lost Continent

From the DVD extras for "The Screaming Skull."