Arachnus

Arachnus, plural form Arachni, are a species of creatures found on SR-388. At the near-top of the food chain, you fight one in Metroid Fusion as a boss.

In Metroid Fusion, you find an Arachnus in the Main Deck. It attacks you either by spitting flames along the floor and rolling down them or by using his Sonic Wave attack. To dodge the flames, hold onto the ledges on either side. If he hits the wall whilst rollingand you are hanging on, you will be knocked off and into his grasp. You cannot avoid the Sonic Wave attack by hanging onto a wall either. To defeat it, use Missiles to hurt the front part of his body, where the shell isn't. If you run out of Missiles, then normal beams will work, but it will take a longer time. Once he turns into a X|Core-X, he will send out a few yellow and green X|X Parasites that will give you more missiles if you don't have any and replenish your stamina. Once you defeat Arachnus, it will give you the Morph Ball ability.