You're opponent is 80 feet tall, bulletproof, and has magical powers, maybe with hundreds of years of experience.
I doubt all of them are bulletproof, as kendra said their skin is tough but they're not invincible
maybe the magic users doe.
I would be more concerned about the calibur needed to actually take one out (probably like a tank shell so good luck getting that)
If all else fails they can still be poisoned and the like so if you can get a lucky hit into the mouth, nose, eye, ect with a potent enough poison tipped weapon you win. (assuming you could get your hands on one somehow, and they're not immune to it)
If they were invincible nobody would bother trying to fight them in the first place. So I doubt that's the case.
Would probably require magic doe.