Golem

Survive a single hit of 500 damage or more. You need the armour and shields to take a big blow and live: Power Armor MK2 loaded with Energy Shields is the classic setup. Then walk into something that hits hard - a behemoth worm's spit, a demolisher's bite, or a big biter - and soak 500+ in one hit without dying. Shields absorbing the hit still counts.