TJ Lavin has spent most of his life in front of roaring crowds—first as a BMX superstar soaring over dirt jumps, then as the no-nonsense host guiding competitors through MTV’s The Challenge.

Some of the challenges that made the top 50 list are Simmotion (which Survivor 45 winner Dee Valladares hopes is the Season 50’s final challenge, she told TV Insider ), the Survivor auction, Smash and ...