Is there a way to add Battle-Bond as in ability in a ROM Hack?

[Nidocito]

I was making a ROM-Hack and I planned on having Ash-Greninja in it. I don't know how to get Greninja to transform after fainting a pokemon.

 

[Dr. Seuss]

Not sure what ROM you're using, so I'll assume you're hacking Fire Red. So far the only way to add it to FR is by using the Complete Fire Red Upgrade. You can check about it by clicking here