Can I just say - I remember bettas but I don't know why he got banned. If he realy does have fish and is considering buying dwarf puffers, we should advise him not to - not just ignore him.
Anyway, you can't keep dwarf puffers with anything else as they'll shred the fins off anything else. Also, they need 5 gallons per fish, excellent water quality and a very well decorated/heavily planted tank to keep them from fighting. They should also be fed small aquatic snails on a regular basis to keep their 'beak' trimmed.