This boss isn't really that hard. You can go in with assault rifles and riot gear and beat the boss with 7-10 players. Bring a ton of bullets and healing brews because the defense units do a good amount of damage. Rockets will take out the overseer super quick. Also bring fur gear because it gets cold in some parts. 3 sets of everything are a must in fighting the boss and units. Thank you.
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!