User blog comment:JmLyan/Jace, the Mind Sculptor/@comment-3974211-20130408163140/@comment-4726614-20130409113338

Could also be :

The mechanic could be made so that if the target can't afford the double mana cost, it instead use all of the mana left. That let the opponent use an escape mechanism or force him to change his combo. Or just back up till the debuff wear down.

You could also put a 1%s low or something like that to the debuff, this way, it can be countered with tenacity. Jace Deals magic damage to his target and apply Concussion for 5 seconds. If the target cast a spell, it cost up to double mana."