Or do you have to transfer from the older game? (can't remember if it was in X/Y or BW2)
You would have to transfer Zen Mode Darmanitan from BW2 as Zen Mode Darmanitan is not available for transfer in XY either. Unless you want to go Dex Nav hunting in Mirage spots to obtain said Darmanitan.
You can actually catch Darmatian with Zen Mode in ORAS in Mirage Spots. As such you can use the DexNav to find yourself a HA Darmatian.