Zilean idea!!!
Hey Balance Team :)
I have an interesting idea for Zilean's passive and W.
The passive can stay like that at 8% aura xp gain (I still think 10% would make s slightly more noticeable impact but I guess it would need to be tested out) At level 18, the Summoner's magic weakens and his Chrono Dysplasia starts to come to the front. He starts to earn a new pool of xp (post lvl 18) starting from 0 xp that just accumulates but converts 1 or 2% of that xp into AP. As he experiences all timelines his power increases but as he has trouble focusing on the present timeline he has trouble regaining his mana, he gets a 50% or 75% basic mana regen penalty.
His W would remain as is but would have an additional passive component to it:
2/3/4/5/6 %XP gain to self
This would make that early game solid support to late game burst mage transition pretty smooth.
Late game he would get a bit bursty, thing he has historically struggled with late game as his damage falls off. Also he would need to better manage his mana or itemize accordingly. If he builds too much AP and no sustain he will have super burst but will need to go to base more often. I think it creates a nice balance.