The Mirror Dimension's appearance is composed of powerful personalities absorbed into it. This means that the appearance of the dimension is always changing, depending on who's soul was "swallowed" by a Deadite. In Army of Darkness vs. Re-Animator, Ash, Sheila, the real Herbert West, and a man simply known as "H.P." are trapped inside the Mirror Dimension, which looks like a twisted version of the Alice In Wonderland story, and Ash's Mirror Dimension counterpart replaces him in the real world. The Mirror Dimension plays a major role in Evil Dead 2: Cradle of the Damned, where Annie Knowby and a copy of Ash are sucked in by a portal instead of an actual mirror, and again the Dimension is themed around a certain story, Adam and Eve in the Garden of Eden, with Ash as Adam and Annie as Eve. The landscape changed again to a simple desert with a bright green sky with odd shapes hovering above the ground.
The horrors of the Mirror Dimension often turn human souls into Deadite souls that can possess the living. When a human's body is taken over by a Deadite they are forced into the mirror dimension, where if they do not somehow reclaim their rightful form, they will remain there forever suffering unimaginable torment.