Now go to the Cargo Hold, where you must lower the water first. This will reveal a planetarium model of a solar system. Interacting with it will initiate an infinite zombie round, which will not stop until you have either completed or failed the step. So make sure you are up for a fight!
Once you interact with the planetarium, the planets will flash in a certain order. Remember this order, take note of it or write it down, as it is the order in which you need to interact with these planets
In case you aren't familiar with the planets of our solar system, here is a helpful picture:
Now head outside, where you can see holographic representations of all the planets and other celestial bodies in the skybox, with the Moon being the actual Moon, and Neptune orbits the boat and passes through sea and icebergs (remember that Neptune was the Roman god of the Sea). Shoot the planets in the order the planetarium showed. When you shoot a planet, make sure to not do any others, because you need to find a blue orb where that planet's alchemical symbol was within a time limit. If you miss the timer or do the wrong planet/do another too soon, you have to start over and possibly check the planetarium again for a new order.
Once the sun is reached, the final blue orb will be in the spawn room and interacting with it spawns ice blocks. Destroy these while traveling to the Poop Deck where the Sentinel Artifact was activated at the very beginning of the match.
When the final ice block is destroyed, a portal will spawn leading to the final boss. Prepare for a grand battle!