The Mimic Master is an Unversed that can be found exclusively as a boss in Kingdom Hearts Birth by Sleep and Kingdom Hearts Birth by Sleep Final Mix. The Mimic Master is fought as the final boss of the Dead Ringer and Copycat Crisis matches in the Mirage Arena. Like the Iron Imprisoner, it cannot be found outside the Mirage Arena.
The Mimic Master is a humanoid Unversed that dresses in a dark blue graduation gown with numerous intersecting bronze highlights. It resembles the Barrier Master Heartless. It also has large cuffs, a white ascot, and black, fingerless gloves. Its legs are not visible because of its gown. Its head is cube-shaped and light steel blue. It has a flat, square crest on its head resembling a mortarboard cap. The tassel hanging from this "cap" is a small, purple sphere attached to a gold crescent moon. This charm hangs from the right corner of the Unversed's cap via a short, gold chain. Its large, red eyes are set in a seemingly happy expression. It also carries a massive, pink book as a weapon.
The Mimic Master has more Unversed emblems on its person than any other Unversed, sporting one on the front of its robes, and one on both covers of its book, leaving it with a minimum of three emblems. Several pages of the Unversed's book seem to be emblazoned with the insignia as well, though others display black and white pictures of Terra, Ventus, and Aqua in their armor.
In Kingdom Hearts Birth by Sleep Final Mix, the Mimic Master receive a palette swap which gives its body a shade of grey, dress in a lighter blue graduation gown with numerous intersecting yellow and dark-purple highlights. It has dark-yellow cuffs, a dark-purple ascot, and grey, fingerless gloves. Its mortarboard cap shape head is now grey with black edges. The tassel hanging from the "cap" is now a small, grey sphere attached to a gold crescent moon. It now carries a purple book.
- Many similarities exist between Number VI of Organization XIII, Zexion, and the Mimic Master. For example, both wield a weapon in the shape of a book. The Mimic Master is also fought in a round at the Mirage Arena that translates as "Magician of Illusion" in the Japanese version of Kingdom Hearts Birth by Sleep, Illusion being Zexion's attribute. The Mimic Master lastly has the ability to take on the forms of others or use others' own abilities against them, something previously demonstrated by Zexion in Kingdom Hearts Re:Chain of Memories during his encounter and battle with Riku.
- The Fakes created by the Mimic Master have names based on the player's, but with the letters scrambled or with extra letters added in.
- The names of both Mirage Arena matches the Mimic Master appears in reference the Unversed's ability to copy its opponent.