New Zilean passive proposal

Zilean would be super fun as a xp hoarder lvl up intensive champion.

I propose a % xp aura at 10% instead of 8% (current) and when Zilean reaches lvl 18 He gains "Chrono-displasia" to his passive which allows for him to continue earning xp and start earning levels backwards (to lvl 17, then 16 and all the way back down to lvl 1) while still increasing base stats and earning 2 or 3 AP per level reversed instead of a skill point.

His base stats earnings per lvl would need to be cut by 1/4 or 1/3 to balance out the accelerated leveling rate.

I propose to add a passive component to Rewind: 2/4/6/8/10 % xp gain to only Zilean. This will make Zileans total xp % gain to 20% with rewind maxed.

This will make items like Rod of ages super effective on him cause he would be leveling faster and 2 times more.

All "per lvl" runes and masteries would just get to lvl 18 (no advantage for the reverse leveling).

This would also synergize well with the inspiration mastery as after lvl 18 he would go down in lvl and be below everyone else.

Quick question in regards to Valor's Reward passive (Rod of Ages): If one earns 2 lvls at the same time, does the passive stack or it just activates 1 time?

I think this proposal would be super fun, can be balanced and super thematic for Zilean.