In order to figure out which character gets what power on joining, I roll a dice, and the number that they receive corresponds with the type of power they get. First I roll the dice once, and this determines whether the power is a major power or a minor power.
1-3-5 Minor 2-4-6 Major
Then I roll the dice again, and this roll represents what category the power falls under. For the Er'Undi, Nature [control of plants, weather etc], Animals [shapeshifting, mind reading, sharing thoughts etc] or Elemental [control over fire, water, earth etc]
For the Er'Undi: 1-3 Nature 2-4 Animal 5-6 Elemental
For the Arcaian it is split similarly. Mind (mind control, mind reading, illusions), Physical (physical strength, agility, speed), and Emotional (empathy, healing etc)
For the Arcaian's: 1-3 Mind 2-4 Physical 5-6 Emotional
Once those two numbers have been rolled then a power will be given.