Both the Magus and Patriarch are psykers, and have the special power Hypnotic Gaze. This can be used in any Assault Phase after all models have moved but before any combat takes place. The Magus or Patriarch locks eyes with one enemy model in base contact with him, attempting to take over his mind! If the Cult psyker passes a Psychic Test, that enemy will need to roll 6's to strike hits in that Assault round. If the test was successful, and the roll is also higher than the enemy's Leadership, then the enemy cannot strike any blows at all – his will has been completely overpowered by the Hive Mind! The Cult psyker can still attack as normal, even if the test is failed.
The power will only work on living creatures – so Vehicles, Demons, Necrons, Thousand Sons, Avatars, Wraithguard, etc. are not effected. Tyranids creatures of any type are not effected by the power either. Note that it only lasts one round – the user will have to test again each new round, but he can test in the enemy's Assault phase as well as his own.