Hm, I think the wording should probably be the other way around. In other words, the card could simply read "Discard King Belshazzar to protect X Heroes in play." Otherwise, you could have Headquarters at Riblah and King Belshazzar in play yourself and protect your Hero(es) (as the cost) and wouldn't be able to discard Bel due to protection from Headquarters. This way, the protection is based on the discard. Unless this was something that you had in mind. Just my two cents. Otherwise, I like the card.
