条件・譲歩N2
〜ものなら
if one could... (but one can't) / if only... (impossible wish)
Structure
V-可能形 + ものなら；V-ようとする + ものなら
Explanation
A hypothesis about something impossible: if it could happen... Used for wishes or threats. Attached to the potential form of verbs or ようとする.
Examples
できるものなら、もう一度彼女に会いたい。
If only I could see her one more time.
逃げようものなら、ひどい目に遭うぞ。
If you try to run, you'll be in big trouble.
Note
① with the potential form expresses an impossible wish; ② with ようとする expresses a threat. Don't confuse with the plain ものなら (= なら).