The transformation Raven takes when she merges with Dusty and Xii, the Sphinx—the whole version of the original mythological Guardian from the perspective of Raven.
"Yes, the other Shifter's guardian can help. Together, you can be whole."
—Bit
Gravity Sphinx is the second transformation that Raven used in Another Story - Raven's Choice. It is the alternative and mythological Guardian whole of Xii and Dusty in their Phoenix and Panther forms before their split into two separate entities, from the perspective of Raven. Only appearing during a cutscene in Episode 6: Unshed Tears, it was used to destroy the Giant Collector.
A similar mythological Guardian, Gravity Gryps, is used by Kat.