Thousand Dragon is a basic Fusion monster, who lists Time Wizard and Baby Dragon as his fusion materials. He has 2400 ATK and 2000 DEF, solid numbers for a fusion monster from those materials. Having these two monsters and a Polymerization could mean big trouble for opponents in the early days of casual Yu-Gi-Oh play. Of course, someone could answer him with a Dark Magician, Blue-Eyes White Dragon, or Serpent Night Dragon. But, removal was at a premium in those days, with Fissure and Dark Hole the most common answers, and Raigeki tough to come by. He was never a very competitive card, but he was fun and quite rare to pull.
As of 10/25/2019, here is where the population of these graded cards stands:
Unlimited - 14 PSA 8, 36 PSA 9, 32 PSA 10
First Edition - 12 PSA 8, 33 PSA 9, 62 PSA 10
Interestingly, there are many more 1st edition PSA 10 examples in existence, but it’s easily the more desirable card. If you’re purely a collector, a PSA 9 or PSA 10 unlimited edition example is fine. If you’re looking for ROI, definitely hunt for the 1st edition PSA 10. It’s a nice card to own just to have a piece of Yu-Gi-Oh history in your possession.