Like most Pokmon cards, the value of Riolu depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (POP Series 8)
Teal Mask Ogerpon ex Prismatic Evolutions #177 Number Supertype Subtypes Rarity Artist HP Regulation Mark Retreat Cost Weaknesses Teal Dance Ability Once during your turn, you may attach a Basic Grass Energy card from your hand to this Pokmon
Regular Pokmon cards for Phione, Applin, and Dipplin are also shown off
Authentic cards feature the classic WOTC cosmos holo, sharp print quality, and proper color saturation
Compare that to Base Set, where the most powerful attackers werent ever 1HKO-ing each other, and many struggled to even 2HKO, which made games significantly slower to the point where deck-out was a common win-condition