It often suggests that the card makes use of one or more materials not present in a genuine card
You must start off with a basic Pokmon and evolve them in order, with the execption of Baby Pokmon
at some point, somebody who has one of the promos will want to sell them, so you can find listings on sites like eBay and TCGplayer
On the other hand, there's Extort, a minor nuisance in 1v1, but a major annoyance for multiplayer due to its ability to stall the game
WotC and Mark Rosewater's design team seemed to have resolved that issue by using the security holo stamp to convey information about the card's legality in specific formats
Theyre a great resource for a lot of different decks, but having to exile a land from the graveyard is just too anti-synergistic with many land strategies to sell me on this card