Root Fossil lets a player put it into play as if it were a Basic Pokémon, counting as Colorless with no attacks and no retreat. The original Sandstorm wording said it counted as a Colorless Pokémon instead of a Trainer card and specified it never counts as a Knocked Out Pokémon, while Legend Maker's wording flipped that to counting as a Trainer card as well but kept the no-Knocked-Out rule, and Legends Awakened's wording reversed course again so being Knocked Out while in play does count as a Knocked Out Pokémon.
Root Fossil debuted in the EX era's Sandstorm and was reprinted three more times within that era, in Legend Maker, Holon Phantoms, and Power Keepers, all with Ryo Ueda artwork. The Diamond and Pearl era's Legends Awakened brought a further Ryo Ueda illustration alongside the reworked wording. Our catalog lists 5 printings.
Root Fossil is based on the fossil item from the Pokémon games that can be revived into Lileep.
The Sandstorm printing is Root Fossil's first release
The Legend Maker printing changed the wording so Root Fossil counts as a Trainer card as well as a Pokémon
The Legends Awakened printing carries the reworked wording and a new illustration
It depends on the printing: the Sandstorm through Power Keepers wordings say it does not, while the Legends Awakened wording says it does.
Ryo Ueda illustrated all five printings.
From Sandstorm (2003) · 1 printing
Play Root Fossil as if it were a Basic Pokémon. While in play, Root Fossil counts as a Colorless Pokémon (instead of a Trainer card). Root Fossil has no attacks of its own, can't retreat, and can't be affected by any Special Conditions. If Root 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 Root Fossil from play.
From Legend Maker (2006) · 3 printings
Play Root Fossil as if it were a Basic Pokémon. While in play, Root Fossil counts as a Colorless Pokémon (as well as a Trainer card). Root Fossil has no attacks of its own, can't retreat, and can't be affected by any Special Conditions. If Root 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 Root Fossil from play.
From Legends Awakened (2008) · 1 printing
Play Root Fossil as if it were a Colorless Basic Pokémon. (Root Fossil counts as a Trainer card as well, but if Root Fossil is Knocked Out, this counts as a Knocked Out Pokémon.) Root 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 Root Fossil from play. (This doesn't count as a Knocked Out Pokémon.)

Root Fossil
Item
First printed in Sandstorm (2003)
Play Root Fossil as if it were a Colorless Basic Pokémon. (Root Fossil counts as a Trainer card as well, but if Root Fossil is Knocked Out, this counts as a Knocked Out Pokémon.) Root 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 Root Fossil from play. (This doesn't count as a Knocked Out Pokémon.)