Zilean double Q combo is too high reward for too little risk.
I know hes not popular or played by skilled players much, but in the right hands hes op as shit.
His double Q combo deals more damage(600+180% AP) than an AP
R+E combo but with an 8 sec cd instead of 100 sec, and it doesnt require the all-in that Malphite does.
I dont know how else to put it, thats just too cheesy.
The only way I can think of adding some skill to this would be reducing the Q initial damage by roughly 1/3 (200+60% AP down from 300+90% ap) and giving him a temporary buff after casting Q that stacked up to 2 times which empowers his next basic attack to deal aoe damage on hit equal to 50% of his Q damage (100+30% ap)
The total damage potential would remain 300+90% Ap per Q, and his double q stun would still function the same, but he would need to basic attack once or twice to deal that insane mount of damage like before.
Futile I know, but I have to try anyway.