Hi! I can only answer this because I just asked the same question yesterday: next to nothing can mix with dwarf puffers. Some have suggested gobies or ottos, but others have given horror stories about the deaths the DPs caused. They go in a species-only tank that is heavily planted to avoid spats between the DPs themselves.
Well my dads got SAP's but not Dwarf Puffers. His SAP's go quite well with his 2 kribs. When they do play around with the kribs the kribs just scare them off. But Dwarf puffers probably wouldn't go with anyone, but i don't know. The best tankmate would be another Dwarf Puffer but even that would be risky because 2 males would fight and sometimes even a female and a male would fight. I suppose you could put some other fish in with it if you have a big enough tank and it's heavily planted. So if so I would probably say Kribensis, Keyholes or Bolivian Rams. There all very defensive when they want to be.