Go to your dungeon and get out reds, blues, and browns/greens. Pick the type of beetle you wish to fight depending on which type of soul you want (red for Magma, blue or Dazzler, brown for Battler, or green for Puff). Enter the arena. Take all the minions and place a marker, then move it all the way back up against the gate. Go over to the beetles, but only to get one, two, or three. If you get too many, lock on to one then back away quickly. The extra beetle will start to fall back, then stop. Let the others catch up, but not touch you. Run backwards until you reach your minions. The reds will already have its health down a small fraction, then the brown or green will begin to attack. You will probably have one or two minions die, so the blue will move in and heal them. Repeat this tactic to kill them all with a maximum loss of one minion. However, you will gain about 50 to 75 Minion Souls.