Mario wakes up in the world of Portal, where rogue supercomputer GLaDOS tests him while plotting to murder him.
At nighttime, Mario starting to get hungry and decided to sneak into a kitchen, where he is not allowed. Mario looks around until he sees a cake. He ate the cake and got knocked unconscious. Mario woke in in a science facility as prison subject "M4R10". He wonders where his cake went and states on how he feels that something is up his ass, which turned out to be his name tag and GLaDOS asked him to not remove it before putting it back in. Mario attempted to escape through the toilet, but couldn't fit through so he jumped, but hit a light and then the radio which played Toad singing "Let It Go", angering Mario. GLaDOS asks Mario if he is even listening to her, but he tells her to shut the f**k up.
GLaDOS tested Mario to place a storage cube to a button, but Mario ends up crashing to a glass wall. With the portal opened, Mario manages to bring a cube out, but his butt ends up blocking the hole. After completing the test, Mario was rewarded with a Portal gun. He thought it was a camera, and used it for a selfie, only to get his face smudged with a gun. He began to have fun using the new Portal gun he has in his hands, making portals so he could fall into the next one. GLaDOS scanned him and got annoyed at how Mario had a lot of weaknesses. Deciding he's "hopeless", GLaDOS lets him pass.