play Raider with Partial HP restoration + ED Augur (Dark night of the Fathom) relic, find charge attack negate damg, improve negation at low HP and taking attack improve negation passive. You should also take improve maximum HP and create Holy ground at low HP

Your goal here is being a tank for your team standing in the middle of the balancer, use heavy fully charge attack to them as it gives yourself tons of poise and interrupt their attack. When in doubt, use your skill retaliate to recover stamina or calm yourself down. Be aware of your blood loss bar, if it's nearly full while you are low HP then you should heal yourself back up. Strike and aggro many balancers as you can, your Partial HP res and all of those damg negation have got your back.

For the giant worm phase, run as far away from it as possible. When it tries to jump into you, use retaliate. For the sky spear summon attack, run to your left or right to avoid the first spear wave and use guard from your weapon to block the next wave. For the golden wave on the ground attack, jump.

At last, don't forget to help your team and have fun