If the copy is a permanent spell, it enters the battlefield as a token
A card can only be in one zone at a time, and which zone its in currently changes how the rules refer to it and how you can use it
Lastly, the Registry allows me to send my collection to card shops and bulk graders, so they can help me find the elusive cards I still need to complete my sets, like that Fighting Energy in a 9.5 from 1st Edition Gym Heroes, which only eight people sent in to grade, and I need to complete my set
Use an old Energy or Common Pokmon card that you have extra copies of
While its plenty powerful, its the effect on perceived barrier-to-entry that really posed a problem because casual players watching Commander games in passing could reasonably assume that they needed hundreds (now thousands) of dollars in Power-9 mana as table stakes, just to join the format