Yes, I know. 2 different Repuation one one page but since they are more or less exactly the same I thought I save some space.
First off, I would like to point out you can only do ONE of these Reputations, the benefits are the same so it all boils down to which one you find easier to kill.
To join up with the Kroffdor Race, go and see Dimedora for the Humans or Reodora, for the Magmars. Then complete the quest Ordeal by Blood, and pick the machine you want to use.
Much more information to come.