A Temporal Snare is a Necron device that warps the fabric of space-time itself, creating a bubble of altered space-time where time flows more slowly for anyone or anything trapped within it. They are only carried by the Cryptek known as Orikan the Diviner.
Each Temporal Snare is a technologically-advanced temporal trap that can severely impede enemy movement once it is activated, whether those trapped within its field are vehicles or infantry.
Thus, even when traversing the smoothest of terrains, once a snare is activated, enemy units can still find themselves moving at a snail's pace from the subjective perception of those observers outside the device's range of effect.
- Codex: Necrons (5th Edition), pg. 57