Just do what syntac did I shot basically anything that was big or threat to his character or his dinos. U don’t have to fight everything sadly if a giga is in a bad spot like how syntac had to deal 2 of them and basically lost some allos. allos are key cause that bleed is a good way to give giga a taste of his own medicine
Don’t bother with ghillie/fur armour, it’s about 130F in the cave and -15F in the overseer’s lair. So bring tek rifles, tek armour, 10-12 tribemates, a Rex or 2 (or 9), some argys to deal with attack drones and 500 element each. You unlock scorched earth after beating him, so yeah. It resets all your progress on the island, so say goodbye to your Dinos before you go kick the overseer’s nonexistent behind. Have fun blowing stuff up!