The Pallas Siegebreaker is a Wanted Bounty that you can collect from Spider on the Tangled Shore. He is one of the enemies who escaped from the Prisoner of Elders, and it is up to you to track him and down and end his newfound freedom. The only clue you are given on the Bounty when you pick it up from Spider is that he can be found on the Tangled Shore.
Finding the Pallas Siegebreaker is surprisingly easy, and you have more than likely met him before, and just not realized it. The Pallas Siegebreaker can actually be found at the Public Event that happens very close to the Spider’s lair on the Tangle Shore.
The Cryopod Public Event involves taking on a couple of waves of enemies, and then a big boss will pop out of the Cryopod and you will need to defeat them. On the Tangled Shore, that boss is the Pallas Siegebreaker.
To complete the bounty, you don’t need to make the event Heroic and can kill the Siegebreaker. This event is tied into a couple of different quests, however, so if there are other Guardians there, it is considered good manners to ask in local chant it anyone needs to make the event Heroic before melting the boss.
If someone does need to make it Heroic, you simply take a third of Siegebreaker’s health, then shoot the leaking vents on the side of the Cryopod to expose some orbs. Throw them at the Siegebreaker, then repeat the process one more time to freeze him in place.
After that, you need to defend the area from some waves of enemies and the Siegebreaker will be transported back to prison. You can then hand in the bounty from your Quests tab in the Director.