In the Space Marine Codex, Librarian section page 56, under the Psychic Hood (last sentence) it says " The psychic hood can be used once each time an enemy model uses a psychic power within range" I was under the impression that I could only try to stop just one psychic power per turn, but another player told me I could use a the Psychic Hood to try to stop as many as were within the 24in range. Seemed a bit over powering if I was able to shut down a Grey Knight psychic round, or another armies psychic powers with just one Librarian.