At the end of your Movement phase, for each TYRANIDS SYNAPSE unit from your army, you can select one friendly GENESTEALER CULTS unit (excluding PURESTRAIN GENESTEALER and PATRIARCH units) and one friendly TYRANIDS unit each within 9" of and visible to that Synapse unit. If you do, that GENESTEALER CULTS unit from your army suffers D3+1 mortal wounds and one model in the selected TYRANIDS unit regains up to that many lost wounds and until the start of your next Movement phase, each time a model in the selected TYRANIDS unit makes an attack, add 1 to the Hit roll.
TYRANIDS units from your army have the following ability:
Catalyst (Aura): While an enemy unit is within 6" of this unit, each time a friendly GENESTEALER CULTS unit makes an attack that targets that enemy unit, add 1 to the Hit roll.