It's really interesting how it works, from what i've seen, it has a chance to go off on you when you summon the pet(s), a chance on them when you summon them, and a chance for each attack they do. I put it in my bruiser on my thugs/dark, and a gaussians chance for build up in my enforcers. If you do decide to put it in a pet teir with multiple pets, it would be done individually to each pet.