Promethean Watcher

The Watcher is a Forerunner Sentinel variant. It is capable of catching grenades with an anti-gravity field and throwing them back at the assailant. Watchers can be carried and deployed by humanoid drones, assisting the latter in combat. Watchers were encountered on the shield world Requiem in summer 2557.

Trivia
The Watcher, along with the Crawler, was first seen in a leaked image from McFarlane Toys. However, it was first mentioned several months prior in Halo: The Essential Visual Guide.

List of appearances

 * Halo 4