This is because this Pokemon can use the attacks of any Pokemon GX or Pokemon EX on your bench, meaning you can fill the decklist with nearly any overpowered Pokemon you'd like
Mewtwo V SA Price History June 2022 (Launch): ~5,0007,000 (~$3550) 2023: Stable at 7,00010,000 Late 2023 (OOP): Climbed to 10,00012,000 2024: 12,00014,000 2025: 12,00015,000 (stable with minor fluctuation) April 2026: 13,00017,800 (~$85120 raw) The card hasnt had the explosive climbs of Giratina V SA or Lugia V SA, but the consistency is notable
It's also worth remembering that TCGPlayer's prices are an average
The card in your hand only has Giant Killer's characteristics, so if the rules required evaluating the legality of casting from your hand before considering Chop Down's characteristics, you would only be able to cast Chop Down at sorcery speed, since there would otherwise be no rule or effect allowing you to cast Giant Killer at instant speed
Bring your best deck and climb the ranks
Particularly due to his -5 ultimate ability