Watcher in the Dark
Codex Supplement: Dark Angels, p. 7
A model equipped with a Watcher in the Dark, may once per game, ignore a single Psychic Power or Psychic Weapon attack that targets the equipped unit. Watcher in the Darks are normally represented by Tokens which may be removed to track its use. Watchers in the Dark Tokens do not count for models slain or combat resolution.