Depends on the puffer. Some are born killers and some are gentle. My puffer picks at snails and hermits, but never kills them. I had a cleaner shrimp with him for the longest time. He would constantly go up to the shrimp for cleaning. But the shrimp passed away. He still sometimes looks for him where the shrimp used to hang out. He never picks at my corals, just bumps into them.
Mine likes killing gobies and crabs, thats all...