CONCEAL/REVEAL

The psyker takes command of the darkness around
them, using it to conceal their kin or reveal any
opponents who skulk in the shadows.
Conceal: Select one friendly Core unit within 18".
That unit receives the benefits of Light Cover.
Reveal: Select one enemy unit within 18". Each
time a model from your army makes an attack,
that enemy unit does not receive the benefits of
cover against that attack.