From Destinypedia, the Destiny wiki
The Io Pyramid is the name used to a massive alien vessel holding position above the Cradle on Io. Like its counterpart on Luna, this vessel is a part of the aforementioned fleet that attacked the Sol System during the Collapse, and are fragments of the Darkness. This vessel acted as a vanguard for 3 other Pyramids that arrived across the Sol System shortly after it. Asher Mir theorized that the Pyramid arrived on Io to study the Vex.
Overview and layout
Like its brethren, the outside of the Pyramid's hull is covered in segmented panels that vary in pattern, with some having vertical lines and other with patterns resembling circuitry. Much like the Traveler, the surfaces of the Pyramid seem to be composed of some form of rock-like material, occasionally having an uneven or chiseled appearance, giving the ship an almost handcrafted quality. In contrast to its Moon counterpart, the Io Pyramid is rougher in appearance, suggesting more wear and tear to its hull.
The Pyramid can be accessed by an opening along its lower hull. Unlike its Moon counterpart, it is unknown if there is a habitable interior within, but the Pyramid's attempt to pull the Guardian into itself suggests there possibly is one. It is constantly firing a tractor beam underneath its hull that is corrupting the Tree of Silver Wings with Darkness energy.
Season of Arrivals
Following the destruction of the Almighty, the Io Pyramid began to make a move on Io, as its approach was immediately flagged by Rasputin. The Warmind attempted to neutralize the Pyramid with his Warsat network, seemingly achieving victory as the Pyramid disappeared from his radar. Rasputin's victory was short-noted however, as the Pyramid reappeared instantly on the radar, before completely wiping out Rasputin's systems and disabling his core.
The Io Pyramid then arrived on top of the Cradle, pushing the Vanguard to send the Guardian to investigate. Upon the Guardian's approach, the Io Pyramid initiated a gravity lift as the Lunar Pyramid had done before, where it began to speak to the Guardian and expand upon what it had said on the Moon, before suddenly being cut off by Savathûn, the Witch-Queen, as she sent the Guardian spiraling into her Court through a portal, where they eventually escaped.
Weeks after, the Pyramid deeply corrupted the Tree of Silver Wings within the Cradle, as Eris Morn and the Guardian collaborate to intercept and interpret the Pyramid's messages using the Seed of Silver Wings. It also deployed a large force of Pyramid Scales out to survey Io's surface, in order to presumably prepare it for terraforming.
Upon defeating Nokris, Supplicant to Savathûn, the Pyramid on Io finally pulled the Guardians inside, telling them there is an ancient power deep beneath the surface of Europa and that it must be embraced, displaying each race with a shadow of a Pyramid, with one shadow lingering over the Fallen.