In my personal experience, killing these guys is pretty easy if you have the right equipment. You can use a good pump shotgun (mastercraft or ascendant) and just pump these guys full of lead until they die. You can do this off the back of a griffin or by trapping it using metal gates. Weaker shotguns will also work but you will need more ammo. Killing gigas with tames is almost never a good idea since the giga deals a lot of damage and gives your tames a bleed effect that drains a percentage of their health.

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