During the climactic battle, Mirage (Pete Davidson), who's friendliest with Noah throughout the movie, seemingly gives his life to protect his new friend, just like he promised Noah's brother he would. However, to give Noah at least somewhat of a leg-up on battling Scourge (Peter Dinklage), Mirage gives himself over as armor for Noah, essentially providing him an Iron Man suit so that he can fight alongside the other Autobots. From that point, it's unclear if Mirage sacrificed his life to do that, but the mid-credits scene reveals all.
The sequence shows Noah in a garage with Reek (Tobe Nwigwe). To Reek, Noah's simply working on a car that has a pretty funky color palette. However, not everything is as it seems, as Noah asks the car to reveal itself, and it takes the form of Mirage, much to Reek's disbelief. He somehow managed to survive the assault he suffered from Scourge, suggesting he'll be back in any prospective "Rise of the Beasts" sequels.
It's obviously hard to kill an Autobot. Bumblebee died early on in the film, only to be revived via Energon during the final battle. It's not stated if Mirage also had an Energon boost to make it out all right by the movie's end, but his survival will be welcome for fans of Pete Davidson's vocal performance.
