Zetter 99 is the result of the combination between Zetter and his support unit, Double Nine. He can then further combine with Gunber 01 and Father's remaining support machines to form Zetter Gunber.

It is the result of the combination between Zetter and Double Nine. There's no more information available on this form since it doesn't make an appeareance in the game.

Zetter 99's finishing technique, using the Double Nine's main wing section as a boomerang.