The Unknown Fusion Gem, which was shown in "Historical Friction" in a play performed by Jamie and Steven, is a fusion of some of the Crystal Gems, although it is unknown which Crystal Gems fused to make her.
In a play about William Dewey, he was saved by an unknown Fusion Gem from a giant Gem Monster. While the silhouette from the play gives a very basic idea of her physical appearance, the rest of her characteristics are too obscure to define.
Her lower body and upper torso appear to be reminiscent of Garnet. She also sports a huge mane of hair but kept in a proper hairstyle closely resembling that of Rose Quartz. Four arms depict her while the Temple Fusion has eight arms, and Alexandrite has six.
In the play, she is portrayed as towering over William Dewey, his ship, and its crew. Whether or not this is an actual attribute of hers or simply an artistic choice by Jamie remains unknown. However, the final script was edited by Pearl for accuracy.
In Mayor Dewey's original script, William Dewey replaces this Fusion Gem. Dewey describes his ancestor as "growing to fifty feet tall," implying this fusion was that tall.
- In Mayor Dewey's original script, his ancestor William Dewey performs the actions of this Fusion Gem.
- In the book "Keep Beach City Weird: You Can't Hide the Truth!!!", Ronaldo Fryman mentions that this fusion bears some resemblance to the Crystal Temple.