Oracle

An Oracle is a Vex that appears in the Vault of Glass and the Wolves' Gambit.

The Templar
During the fight against The Templar, Oracles will appear as yellow balls of light and spawn in various locations across the room. Failing to kill one in time will result in the whole fireteam being marked for negation. Marked players will die when The Templar casts the Ritual of Negation.

Atheon, Time's Conflux
When Atheon opens the timestream and sends three Guardians into one of the portals, seven red Oracles will appear to those three Guardians. Killing all seven Oracles will grant the entire fireteam the Time's Vengeance buff, which greatly increases the damage done to Atheon and surrounding Supplicants.

On Hard mode, if a Praetorian takes control of a Sync Plate during the fight with the Gatekeepers, a red Oracle will spawn above the Sync Plate's corresponding time gate. If the Oracle is not killed within a certain period of time, the entire fireteam will be killed.

Oracle Disruptor
Upgrade on weapons received as loot from VoG. All raid weapons (that have the perk unlocked) will hit for an additional 499 damage (regardless of attack stat).
 * The perk is not applied on every shot because it's a fixed damage amount.
 * The perk likely has an internal cooldown, meaning it can only be applied so often.
 * Testing shows that the internal cooldown appears to be between 2 (lower bound as a shot at 2 seconds and 1 frame did not proc it) and 2.7 (upper bound as a shot at 2 seconds and 21 frames did proc the effect) seconds long.
 * Damage may be dependent on character level and raid difficulty.

Wolves' Gambit
After the Guardian enters the Vault of Glass in the story mission Wolves' Gambit, Variks will inform them that the House of Wolves are attempting to tap into the Oracles. During this phase of the mission, six Oracles will appear, one at a time. The Guardian must destroy them within approximately ten seconds of them appearing, or the Oracle will inflict the Oracle's Cry debuff, instantaneously killing the Guardian.