Okay, I'm helping my friend look for a story and it was described to me secondhand so bear with me... or would it be bare with me? No that would mean getting naked... oh well.

Anyway, apparently it has Harry going back in time.

He uses night-vision goggles to beat a bunch of 5th+ years in a "Seekers' duel" (whatever the hell that is)

And for some reason Pansy Parkinson develops a crush on him cause he used the killing curse on a troll or something...

Come to think of it, I might actually want to read this too...

 

I am pretty sure I've read this before though I don't really remember it. I like to find it too now.

 

I believe you're thinking of HI POWER by The Sage of Toads. However, the story appears to have been taken down, but a note on the author's profile promises it will be back in due course.