Claw Fossil occupies a Pokémon's spot in play as a Basic Pokémon with no attacks that can't retreat or be affected by Special Conditions, and can be discarded from play during its owner's turn before attacking. The Legends Awakened wording reversed the earlier rule so that if Claw Fossil is Knocked Out in battle, it does count as a Knocked Out Pokémon, though discarding it voluntarily still does not count, a subtle but meaningful shift for Prize card math.
Claw Fossil first appeared in Sandstorm in 2003 with art by Ryo Ueda, who illustrated every catalogued printing of the card. It was reprinted through Legend Maker, Holon Phantoms, and Power Keepers in the EX era, and reached the Diamond and Pearl era in Legends Awakened, giving it a five-set run entirely under one illustrator. From Legend Maker on, its text says it counts as a Colorless Pokémon as well as a Trainer card, where Sandstorm said instead of a Trainer card. The Power Keepers text differs from Legend Maker's only by a missing comma.
Our catalog lists 5 printings of Claw Fossil across 5 sets, all Common rarity, spanning from Sandstorm in 2003 through Legends Awakened in 2008, without any rare or secret treatments among them.
Sandstorm printing is Claw Fossil's first appearance, illustrated by Ryo Ueda
Power Keepers printing is the last of its four EX era printings
Legends Awakened printing introduces the reworded Knocked Out rule
It reversed the rule so that being Knocked Out in battle counts as a Knocked Out Pokémon, though voluntary discarding still does not.
Ryo Ueda illustrated every catalogued printing of the card.
No, it can't retreat and can't be affected by any Special Conditions.
From Sandstorm (2003) · 1 printing
Play Claw Fossil as if it were a Basic Pokémon. While in play, Claw Fossil counts as a Colorless Pokémon (instead of a Trainer card). Claw Fossil has no attacks of its own, can't retreat, and can't be affected by any Special Conditions. If Claw Fossil is Knocked Out, it doesn't count as a Knocked Out Pokémon. (Discard it anyway.) At any time during your turn before your attack, you may discard Claw Fossil from play.
From Legend Maker (2006) · 2 printings
Play Claw Fossil as if it were a Basic Pokémon. While in play, Claw Fossil counts as a Colorless Pokémon (as well as a Trainer card). Claw Fossil has no attacks of its own, can't retreat, and can't be affected by any Special Conditions. If Claw Fossil is Knocked Out, it doesn't count as a Knocked Out Pokémon. (Discard it anyway.) At any time during your turn before your attack, you may discard Claw Fossil from play.
From Power Keepers (2007) · 1 printing
Play Claw Fossil as if it were a Basic Pokémon. While in play Claw Fossil counts as a Colorless Pokémon (as well as a Trainer card). Claw Fossil has no attacks of its own, can't retreat, and can't be affected by any Special Conditions. If Claw Fossil is Knocked Out, it doesn't count as a Knocked Out Pokémon. (Discard it anyway.) At any time during your turn before your attack, you may discard Claw Fossil from play.
From Legends Awakened (2008) · 1 printing
Play Claw Fossil as if it were a Colorless Basic Pokémon. (Claw Fossil counts as a Trainer card as well, but if Claw Fossil is Knocked Out, this counts as a Knocked Out Pokémon.) Claw Fossil can't be affected by any Special Conditions and can't retreat. At any time during your turn before your attack, you may discard Claw Fossil from play. (This doesn't count as a Knocked Out Pokémon.)

Claw Fossil
Item
First printed in Sandstorm (2003)
Play Claw Fossil as if it were a Colorless Basic Pokémon. (Claw Fossil counts as a Trainer card as well, but if Claw Fossil is Knocked Out, this counts as a Knocked Out Pokémon.) Claw Fossil can't be affected by any Special Conditions and can't retreat. At any time during your turn before your attack, you may discard Claw Fossil from play. (This doesn't count as a Knocked Out Pokémon.)