Unlike the RGZ-91 Re-GZ, the Re-GZ Custom is a fully transformable mobile suit. The Re-GZ Custom has more powerful weapons and features wing binders similar to the original MSZ-006 Zeta Gundam. The head also resembles the Zeta Gundam's head. It is halfway between the development of the RX-93 ν Gundam and the Re-GZ, and features 28 apogee motors on the body. It possesses an improved design of the back weapons system used originally on the Re-GZ.
The RGZ-91B was developed specifically for use by Amuro Ray, but with the completion of the RX-93 ν Gundam, the project was shelved.