I had a baby guppy live with the puffer for awhile. The puffer knew it was there and never bothered it. The guppy got bigger too. And it seemed the Puffer accepted it cause the puffer never bothered to lunge at it even if it was right in front of it's face. But I eventually took the guppy out. Everything else I have put with the puffer has been destroyed. Including guppies, minnows, malaysian trumpet snails, danios, and white clouds.
I didn't mean to feed the puffer fish. These fish I moved to the tank more as an experiment because they were unwanted. I knew the possibility they'd be eaten/killed was high. I thought 4 big minnows that were fast were gonna survive awhile. Nope, the Puffer destroyed them all in 1 night.