Catalyst

This power may be used once per turn at the beginning of the Tyranid player's Assault phase and requires a Psychic test to use. If the test is successful, the Tyranid player can nominate a single Tyranid unit within 24" of the creature using the power. Models in the affected unit will strike back in close combat even if killed before their turn to attack in Initiative order. The dead models are removed once they have made their attacks.