Tyrant Reserved Cards

Tyrant cards found in this category have their selling restricted. Whenever you have a certain number or less of these cards in your unused card pool, selling of them is disallowed.

The T-46 Leonidas, additionally, cannot be sold at all after a bug that allowed you to get another each time you refreshed, combined with the sell price of 100 gold per, could have allowed an infinite amount of gold to be procured.