N2
ものなら①
If, If one could, If something would be possible
俺のことを捕まえられるものなら、捕まえてみろ！
Catch me if you can!
Explanation
「ものなら①」 has 2 uses
1A wish that can't come true
About something you can hardly do, followed by a wish such as 「たい」: 「戻れるものなら、子供の頃に戻りたい」 (if only I could, I'd go back to my childhood).
すぐに直せるものなら直したいけど、今はちょっとお金がないから厳しいかな。
If it can be fixed soon, I'd like to fix it, but it might be tough right now because I don't have money.
もし行けるものならケニアに行ってみたいです。
If it's possible, I would like to go to Kenya.
2A dare
You're sure the other person can't, and you dare them, with 「てみろ」「てみなさい」: 「やれるものなら、やってみろ」 (go on, try it if you can).
私よりもっと上手くやれるものならやってみろ！
If you can do this better than me, I'd like to see you try.
俺のことを捕まえられるものなら、捕まえてみろ！
Catch me if you can!
Mixed up with
「ものなら」① (this one): potential form, 'if one could do this very hard thing'; followed by 「〜たい」 or 「やってみろ」.
「ものなら」②: dictionary form, 'if you ever do it, something terrible follows': 「遅刻でもしようものなら、厳しく叱られる」 (If you were late, you'd be scolded harshly).
The two differ in both form and meaning.