Remove the Bishops From the Board
This achievement is far more difficult to unlock than the other kill total achievements. This is because Watchers only appear in the final game of the Collection, Halo 4, and are also the least numerous of the Promethean enemies. Watcher kills are easiest to accumulate in Spartan Ops, specifically in the chapters The Challenge, Clean Up, Spartan Miller, Nothing Can Go Wrong, Science Mountain, and Out the Other, all of which feature more than twenty Watchers.
- The name of this achievement is a reference to the Promethean Watcher's original name, the Bishop.