User blog comment:Xyclone010/CCC4: Lustrum - The Time Mage/@comment-3974211-20140708142219/@comment-3974211-20140709105829

"...one of her basic abilities she empowers the next cast of that ability..." The empowerment would only apply to each individual ability. I was thinking it would have a counter similar to Kassadin's ultimate, except instead of mana cost it shows the current empowerment stacks.

However, I completely misunderstood your passive - my idea shouldn't even be considered. I think 1.5 seconds is a very small window, though. I think it's more likely people will accidentally cast the ability early and end up losing all their mana. Maybe half the cooldown for double the cost? :P