The general orientation is to make Zilean feel better as an ability power focused mage that has interesting gameplay instead of spamming bombs with q+w+q and strolling away in trolling happiness. I also tried to preserve the supportive side of Zilean by giving 3 of his abilities ally and enemy cast effects providing for tons of decision points throughout the game. The passive is not the best it can be but i ran out of ideas so read and comment please. (The formating also isnt the best it could be but i tried).
ps. i also thought that the ultimate a large aoe "chronostorm" that damages enemies every second and stuns them if they are affected by zileans q or w when it hits them but it seemed too viktor/kennen style