- Main article: Armor Fossil (Mysterious Treasures 116)
The Armor Fossil was introduced as a Trainer card in the Pokémon Trading Card Game in the Mysterious Treasures expansion, first released in the Japanese Secret of the Lakes expansion. Although it is a Trainer card, it is played as if it were a Colorless-type Basic Pokémon, meaning the player's opponent takes a Prize card when it is Knocked Out. However, Skull Fossil can't be affected by any Special Conditions, can't retreat, and the player may choose to discard it at any time during their turn. Additionally, if it is damaged by an opponent's Pokémon's attack, it allows the player to flip coins until they get tails and, for each heads, reduce the damage done by the Attacking Pokémon by ten. It can evolve into Shieldon that evolve from an Armor Fossil.
During the XY Series, the Steam Siege expansion included the Item card Armor Fossil Shieldon. It allows players to look at the bottom seven cards of their deck, reveal a Shieldon they find there, and put it onto their Bench. The other six cards are then shuffled back into the deck.
Armor Fossils are also featured on Unidentified Fossil cards. These cards are played as if they were Basic Pokémon and can evolve into Shieldon.