Pick 3 things that no one else in the world could beat you at all 3

1. Sub 4 mile. Got ya there
2. Rock climb a lot (V7-V8 boulder level), so definitely well above average grip strength (would probably cook you in a test of grip strength like a dead hang)

3. Spatial analysis = Top 0.05% in the world in Fortnite, a game where fast spatial analysis, not reaction time, is the key to succeeding

Our battle will be legendary

1. Tanning

2. Single Arm Bench Press on a Smith Machine

3. Claiming I am stronger than every track athlete in history on a track message board

This guy's doing it right with his #2. The key to this game isn't being impressively great at something loads of people compete on. It's finding something super niche that hardly anyone else does at all.

For example, I'm really good at math. Easily top 1%. But that is 1% of *all people*, which is still 80 million people. Meanwhile, I also play with a kendama sometimes. What's that? Exactly. I'm kinda bad at it, but way better than someone who's never played with one. This is probably more useful for this game than my math abilities.

One more thing to note - being 99.9% at three totally unrelated things isn't actually enough. This only gets you to 1 in a billion, even assuming independence. But I think the independence assumption is very optimistic - achievement, and especially extreme achievement, tends to correlate across domains. And probably even more so for the buckets you've chosen. Even things where this might not be obvious, like running and data science, or running and hockey.

So anyway, to be confident you probably need to be like 1 in a million or better at something, and the way to do that is to find something niche.