Azelf - This Pokemon allows you to rescue a critical Pokemon-- perhaps a card you only run 1 copy of, such as a Level X or a tech like Dusknoir DP, or part of a line that you need to swarm, such as Beedrill-- from your Prizes, which is invaluable
Collecting these was pretty much the only thing to do once you beat the game and bought all the house decorations, so I got pretty far in getting all three variants of each card before I moved on to other games
His team consists of Dragon Type Pokemon, and his special move is Dragon Tail
The special foiling, the lore pips across the card, there's so much making this card beautiful that it's no surprise it's so expensive
One is designed to let you Synchro Summon while you Synchro Summon, while the other is stall incarnate
2 cards featuring new variants of Venusaur, Greninja, Haunter, Onix, and Jigglypuff