If you’re trying to kill this bro for the achievement, here’s how I did it. Get yourself a Quetzal with a platform and put about nine auto turrets on it. Put about 100 bullets in each turret and find yourself a Giga. Make sure the turrets are on high range and turn them on as soon as you’re close to the Giga so you waste as little bullets as possible. Just start circling the Giga and stay out of the hit range. Boom, dead Giga in about five minutes.
If one is encountered near water, you can simply lure it out to sea with a flyer and it will swiftly drown. Given the water is deep enough. If encountered inland not near water. Pray to the overseers you have something fast enough to out run it. Then promptly die because they're as fast as a mad Hispanic mother with a shoe. Not as deadly as one though.