To those of you having trouble with the Robot Boss, use the White Magic "Seal" to stop it from regenerating itself. If you don't, the fight is nearly impossible.
Guidoido, you need to create one unit of every element on a single map. This means you can have Fire, Cold, Energy, and Poison be either Mages or Dexers. You need Physical, so that HAS to be a Dexer, since Physical can only be dealt by Dexers.