u/Agent_Lei

Fighting with the melody - Jimmy Urine

https://youtu.be/4SCQVGQaDfs&t=18

it starts at 0:18 and ends at about 0:33

It's the arpeggio synth

let me know if I missed anything

https://youtu.be/4SCQVGQaDfs&t=19
I also remember it being in the portal 2 ost
if yall have a better subreddit for this let me know