- 化石 (base)
- かせき (ruby)
- Kaseki (romanized)
- 化石 (Hanja)
- Hwaseok (romanized)
"Fossil" (化石 Kaseki) is an archetype of EARTH Rock Fusion Monsters. It was used by Jim Crocodile Cook in the Yu-Gi-Oh! GX anime.
A number of older cards, such as "Fossil Dyna Pachycephalo" and "Fossil Tusker", include "Fossil" in their English names but are not part of this archetype, as their Japanese names do not contain 化石. However, because TCG and OCG support for this archetype only works on Fusion Monsters, this is not an issue.
The "Fossil" archetype was a candidate to be released in Collection Pack 2020, via a poll. The archetype came in first place, with 27.4% of the total votes.
The Fusion Materials of the "Fossil" Fusion Monsters, and hence mechanics of the Deck, is different in the various media the cards appear in. In the anime, the Rock monster must be banished from the player's Graveyard while the other monster must be banished from the opponent's Graveyard and have a specific type. In the Tag Force games, the Graveyard and Level requirements are the same as the anime, but they do not require the monster from the opponent's Graveyard to be a specific Type. In the OCG/TCG the materials were simplified again: No specific Types are required, but each series of monsters has a different restriction on which monsters need to be in whose Graveyard.
In the Japanese version, the "Fossil" Fusion Monsters each include the geologic era from which they originate in their names. In the anime and some video games, "Time Stream" supports "Fossil" Fusion Monsters based on the era in their name. The "Cenozoic" monsters are all Level 4 monsters that require a Level 4 or lower monster as material; the "Mesozoic" monsters are all Level 6 monsters that require Level 5 or 6 monsters as material; the "Paleozoic" monsters are all Level 8 monsters that require Level 7 or higher monsters as material.
The Fossil "Dragons" all require monsters from the opponent's graveyard, whereas the Fossil "Machines" all require Rock monsters from your GY. All the Fossil "Warriors" can do with either or.
The Fusion Monsters all can only be Summoned by the effect of "Fossil Fusion", which banishes monsters in both Graveyards as Fusion Material. The Fusion Monsters all require a Rock monster and a monster of a particular Level to be used as material.