Imprisoned
This die captures any number of opposing characters with a total fielding cost of 2 or less. This effect lasts until canceled or you damage your opponent (return the captured die to the field).
Magneto - Hellfire Club
While Magneto is active, if your opponent has no Villains in the field, he takes 2 damage each time he draws one or more dice from his bag.
If I have Magneto fielded and my opponent has no Villains in the field he takes 2 damage when he draws dice from his bag. Does this damage count as me damaging my opponent, releasing captured characters from Imprisoned action die? Am I considered the source of the damage, or is it similar to the lose 1 life rule when not enough dice are available.
Uncanny X-Men rulebook page 6
If, after refilling the bag from the used pile, you are still only able to draw 3 dice or fewer, lose 1 life and gain 1 generic energy for each die below four that your drew. For example, if you drew only two dice from the bag, you would gain 2 generic energy and lose 2 life.