They are legal in all competitive formats and play exactly like the standard version
Somehow, the excitement still doesnt stop there, as Wizards has now confirmed the Bonus Cards that can appear within the new Secret Lair drops
Both she and the alternate commander, Celes, Rune Knight focus on milling cards to the graveyard and then reanimating creatures to fill your battlefield
I personally always bring my own basic land cards to the prerelease, and Im going to recommend you do as well (if you have some)
Although she wouldn't be able to quest again immediately without another card to untap her, her continuously bouncing back to the table will frustrate other Disney Lorcana players at the very least, as she will keep resurfacing for the entire game
The aggressive playstyle of Amber pairs well with the card draw opportunities that Amethyst presents, and it can be a difficult deck to deal with once it starts flooding the board with characters