LionFish says.......
You see, a cowfish is not a Puffer, but it is a Boxfish. And just so you know, boxfish contain a poison that can be released into the water. This poison can kill anything. If it gets spooked or scared it will release the toxin. I try to avoid most Boxfish species because they are big risks. With a 100 gallon tank, I don't see why it wouldn't work with 2 puffers. Depending on the size of the ppuffers and the time you put them with eachother. I have seen several puffers together living peacefully, so I would say it is possible.