Sitting at 10-0-1 in 1995 3 UFC tournament championships under his belt, Royce Gracie was far and away the most popular MMA/NHB fighter at the time. Royce fought to a draw at UFC 5 with Ken Shamrock and wouldn't fight again until a Pride match-up with Nobuhiko Takada at the Pride Grand Prix 2000.
Here is the challenge Royce issued to Mike Tyson that was pending on the Gracie family website in 1997. The Gracie family had open challenges against those in other martial arts disciplines throughout the 1990's as seen below. (click to enlarge)
Here is the classic Gracie Challenge no holds barred fight between Royce Gracie and Jason Delucia. Delucia turned in a solid NHB/MMA career going 33-21-1 with wins over Masakatsu Funaki, Chris Lytle, Minowaman and Takafumi Ito.