This is surprising for two reasons: firstly, most promotional cards, especially those which have a gimmick such as this one, tend to retain their value over time
Many Japanese releases are exclusive to Japan, feature unique alternate art versions not available in English, and come in smaller print runs that make them more collectible over time
When Setting his card ("Rare Metal Soul"), Tristan was only shown making a sweeping gesture with his right arm, with the Set card materializing on the field afterward
Which brings me to my next point
While everything within the card is in color (black creates zombie tokens, green is primary in must be blocked if able, both colors can grant indestructible, and every color can care about equipment), powering up while equipped is almost exclusively seen in red/white