Crystal Godzilla was a kaiju created for the unmade film Godzilla vs. NeoGodzilla (1994).
Crystal Godzilla was Created by Shinichiro Kobayashi for the unmade film Godzilla vs. NeoGodzilla, the original iteration of Crystal Godzilla would be the first Godzilla doppelganger to introduce the idea of a "crystal life form" fused with Godzilla's cells. A space-born monster capable of metamorphosing, Crystal Godzilla would have been a formidable foe to the earthbound Godzilla, though not many details of what the monster is capable of are known. This character would eventually become Space Godzilla after many revisions.
In 1995, "Crystal Godzilla" would resurface - but in a radically different form. Acting as the third form of Ghost Godzilla in Godzilla vs. Godzilla (Story Plan A), this next iteration of Crystal Godzilla created by Kazuki Omori would literally be the 1954 Godzilla with a semi-transparent, crystalline figure, formed from the dust of one of its bones. A revived Little Godzilla would later do battle with this new version of Crystal Godzilla. Outside of the name, it shares no similarities with it's 1994 precursor.
The first incarnation of Crystal Godzilla was designed with a Space Form, a Combat Form, and a Mature Form. The Space Form would be encased in a thick layer of crystals and could quickly travel through outer space. The Combat form would have Crystal wings on shoulders, and crystals on body that could expand or contract. The Mature Form would look very similar to the Combat form, but with added layers of crystals on it's chest, legs, and head to increase defense.
No official concept art exists of the 2nd version of Crystal Godzilla, so information on it's appearance is quite limited.