The Gorgons
Deep in the Vault of Glass, the fabric of reality bends to the will of the Vex. Warlocks speak in tones of awe of the Gorgons - creatures that seem to possess a dreaded, almost unimaginable strength: an ontological weapon.
Like the Oracles and the Templar, the Gorgons reputedly possess the ability to define what is and is not real. Whatever they perceive becomes subject to erasure at their will. Until a countermeasure can be found, Guardians must avoid their gaze at all costs - or reply to any detection with immediate, overwhelming force.
The Gorgons' ability must be tied to the nature of the Vault of Glass. We can take some solace in the clear fact that the Vex cannot manifest this power in the world outside.