Nemesis jumped on the 2nd heli on the right side, went next to the plane where I can barely see the Helicopter, still shoot it and it just doesn't break. I shot down all other incoming Helis but nothing worked.
His name is Ustanak. And I'm not exactly sure what you're describing.
You know the part with the plane and the turrets right? He was in the middle, I shot the Helicopter down, he jumped to his left, to the next Helicopter, then I shot him like 10 minutes and he wouldn't die and the Helicopter wouldn't go down. Besides, the Helicopter was directly right of the Turret and it looked sort of wrong.
I was wondering if I did something wrong or the game glitched?
The helicopter he is on is always stronger than the other ones. You need to try and divide your shots so you weaken an empty helicopter significantly, take out his, and then take out the other one as soon as he hops to it. It can be tricky sometimes.
best way is to target the helicopters he is not on to the point were they are on fire, then focus on his helicopter till it sets on fire, now that all three are highley damaged, you should have enough time to wipe out all the helicopters before any respawn, so take out the other choppers and then finally his one.
Alternativley if you have plenty of magnum or explosive grenade launcher rounds you can take him out with a few shots to the chest depending on what damage skills are applied. For example, Magnum master + firearm L3 make short work of him and he can be wiped out within 10 seconds or so of him getting up to eye level.