Promethean Watcher

The Promethean Watcher is a Forerunner Sentinel variant. Watchers are part of the mechanical Promethean forces created by the Ur-Didact near the end of the Forerunner-Flood war as a desperate attempt to combat the Flood. Watchers acted as the primary defensive drones of the Promethean shield world Requiem, where they were first encountered by the UNSC in summer 2557.

Overview
In the battlefield, Watchers act in a supporting role, assisting Promethean ground units with aerial combat screening and often forcing opponents to engage the Sentinel first. Each Promethean Knight unit carries a single Watcher or more in the back of their armored carapace, from which the Watcher can be deployed at will. Watchers are essentially low-level ancillas based on the Promethean Knight from which they originate. The watcher's AI is housed in its upper carapace above the "head".

The Watcher is capable of healing and augmenting damaged allies, providing them with hard light shields, and can catch and return enemy ordnance, such as grenades, with a gravity-displacement field. They are armed with a built-in Boltshot. Watchers can resurrect destroyed Knights from the small orb of light they leave behind upon death; however, this can only be performed once for each individual Knight. They are also capable of summoning Promethean Crawlers to the battlefield by conjuring the Crawlers' forms from raw material in the ground. Watchers are also capable of building focus turrets.

Appearance
Unlike the angular appearance of most Sentinels, Watchers have curving carapaces, a defining characteristic of Promethean war machines. They have a number of appendages, including what appear to be legs hanging below the midsection which serve as stabilizers and two large disks on both sides which provide agile lift systems and a coiled energy expenditure from within them. Most of these segments lack physical joints and are held together by energy fields. Above the midsection there appears to be a head with stylized facial features and also two fins which act as motion curators to control movement. Like the other Promethean constructs, Watchers under the Ur-Didact's control possess orange lighting, in contrast to the blue-lit appearance typical of other Forerunner constructs.

Trivia

 * The Watcher, along with the Promethean Crawler, was first seen in a leaked image from McFarlane Toys. However, it was first mentioned as the "Watcher Sentinel" several months earlier in Halo: The Essential Visual Guide.
 * The Watcher was called Bishop during the development of Halo 4. The Watcher's model filename is still called "storm_bishop". The Knights are all that survive of the formerly chess-piece-named Prometheans.
 * The Halo: The Master Chief Collection achievement named Remove the Bishops From the Board, which is unlocked by destroying 1000 Watchers, is a reference to the Watcher's original name, the Bishop.
 * An outline of the Reclaimer symbol, in reality the Marathon logo, appears on the Watcher's midsection despite Bungie owning the rights to the Marathon franchise.
 * Shooting the tiny face on the Watcher counts as a headshot and destroys the whole body. However, the face is so small and the Watcher is protected by weak shields, that aiming for it is not very practical.
 * Promethean Knights are capable of deploying multiple Watchers from their body, not just one. This may be due to bugs.
 * Watchers can be assassinated in Halo 4, but not in Halo 5: Guardians.
 * Watchers are capable of catching player thrown grenades and throwing them back. They can also, as of Halo 5: Guardians, catch and throw back the projectiles shot by Hydra Launchers.

List of appearances

 * Halo 4
 * Spartan Ops
 * Halo: Silentium
 * Halo: Escalation
 * Halo: Spartan Strike
 * Halo 5: Guardians