Purple nodes (nodes that convert an empty node) are dropped by the Greater Sphere; one for kill, two for overkill. Red nodes that activate said Spheres are dropped the the Earth Eater; one for kill, two for overkill. This is the ONLY way to obtain more of these Spheres, besides plot events.

Earth Eater has about 1.35 million HP, while the Greater Sphere has 1.45 million.

Beware, for there is a chance that the drop will be a Dark Matter (one for kill, two for overkill), approximating between 12.5 and 25%. If you have already activated Nemesis, it means you should be ready to fight both of the Creations for prolonged periods of time.