Does Black Bolt really have to receive damage from his second special attack?
Honestly I think Black Bolt could be much better. I don't think that the damage and effects caused by his second special attack is worthy to sacrifice 5% of his health. I think this penalty is totally unnecessary and removing it will not unbalance the game.
In case you don't want to remove the penalty, at least make it worthy, increasing and improving the damage and effects caused by his second special attack.