base set booster box 1999 Looking Back At The Legendary Pokémon Release released in 1999 Pokemon Base Set 1 Unlimited

Bronzong #15Rare $14.15 Magneton #43Uncommon $0.46 Dugtrio #19Rare $1.05 Electrode #34Uncommon $0.37 Aggron #1Holo Rare $10.28 Ambipom #13Rare $0.70 Tentacruel #50Uncommon $0.59 Yanmega #54Uncommon $0.34 Lickilicky #38Uncommon $0.56 Haunter #35Uncommon $12.36

He also appears as a dynamic pet asset on Arena

Axebane Ferox

UR Ultra Rare Fire King High Avatar Kirin X FIRE Level 8 [ BeastEffect ] ATK 2400 DEF 200 During the Main Phase, if this card is in your hand (Quick Effect): You can destroy 1 other FIRE monster in your hand or face-up field, and if you do, Special Summon this card

One-off sales can be caused by flukes of circumstance or particularly urgent buyers, so valuing a Mewtwo card is more appropriately done by looking at their average resale value on sites like TCGplayer and PriceCharting (all listed prices are from the time of writing)