His UR drop is Panther Warrior, but not only he doesn't play the card, he also never use it in both anime and manga, or any other game.
Super Roboyarou on the other hand, was his Deck Master in the Virtual World arc of the anime.
But then there's also the strange case of Gagagigo being special for Tristan when again, he never use the card in both anime and manga, or any other game.....
You're wrong on the Gagagigo point. It was the ONLY monster he ever used in the manga. (He never dueled in the manga, but he did use it as a spirit in the memory arc.)
As for Panther Warrior... I'm not at all surprised Super Roboyarou wasn't Ultra. It's not an especially strong card, and the fact Super Robolady also exists made it far less likely. My guess is that his "signature card" will be Command Knight if he's ever available. As for Panther Warrior... Not too surprised he got a Joey card as a drop, but I do wonder why they chose Panther Warrior over Unity.
To be fair, I forgot anyone else besides Joey used a spirit in the memory arc XD
All I remember was Joey using REBD, which is notable because the physical card is most likely still with Yugi at that time, as there's no way Joey can win that duel against Yugi.