Game Grumps and its spin-off Steam Train are gaming shows on Polaris, where a company of people arrange a series of Let's Plays together. It was originally created by Jon and Arin, but then were joined by Ross, Barry and Suzy. Jon was replaced by Danny on June 25, 2013. All of current Grumps members are known friends of Mark. They and Mark reference each other in some videos. Mark has been a special guest on one of the Game Grump shows on Polaris, called Table Flip. On Table Flip, Suzy and Barry get special guests to star in the show dressed like people from the Victorian-era to play board games. It is known that Suzy and Arin are married, as well as Ross and Holly. Danny and Brian forms rock band Ninja Sex Party.
- During their playthrough of Five Nights at Freddy's 2, they called Mark at midnight to receive some advice.
- In "WHAT AM I...?" Mark mentioned that he visited Ninja Sex Party's concert during his Comic Con 2014 trip.
- Suzy and Mark starred together in Big Maker 6 promotional video for the Disney movie Big Hero 6.
- From 5th till 31st of January, Mark was residing in The Grump Space due to his internet problems. Mark was also unable to play with headphones. From then on until October 2015, Mark recorded there but now records his videos at his own house.
- Kevin Abernathy joined Markiplier for a shot of whiskey at the beginning of "NEW SPECIAL GUEST! (5th and 1st Shot)".
- Mark, Matt, and Ryan appeared on the Grumps' Crisis Textline charity livestream. During which, Mark called Momiplier as his punishment for spinning the Punishment Wheel.
|Fischbachs||Mark Fischbach | Tom | Sunok | Cliffton Fischbach | Dee | Chica | Buddi|
|Aaron Ash | Amy Nelson | Bob Muyskens | Cyndago (Daniel Kyre • Matt Watson • Ryan Magee) | Ethan Nestor | George Barnes (Wade) | Kathryn Knutsen | Sean McLoughlin | Tyler Scheid|
|Recurring Collaborators||Brooke Lawson | CinnamonToastKen | Cryaotic | EatMyDiction1 | Fine Brothers | Game Grumps | Jesse Busemeyer | Jordan Maron | Latin Goddess | LixianTV | Matthias | PewDiePie | Rosanna Pansino | SeaNanners | TheRPGMinx | Zombiemold | Ohmwrecker|
|Others||Jessica Fossey | Caspie1405 | Coyotemation | Cranbersher | Crown Interactive | DidYouKnowGaming? | Dlive | Edge | Hot Pepper Gaming | jacksfilms | JeffKyler14 | markiplierSINGSbadly | MatPat | Octobarian | Polaris | RadicalSoda | Random Encounters | shodleech | Sienna Spalding | SuperMega | Tobygames | Triggerhappy1337 | UberHaxorNova|