Is it alright to mix two or perhaps three different species of puffers into a tank as long as they are introduced at the same time, or will they fight?
Definitely not a yes/no answer. It depends on almost every different variable, which species of puffers, maturity of each puffer, tank size, planned feeding regime, etc.
I have a valentini and Green Spotted in my 72. They don't even acknowledge each other. Though the GSP doesn't like to share food though, other than that, no problems