Hmm, needs ore bold font to ease the reading
Passive: I get the idea your trying to get here, but at level 18 he deals up to 80 TRUE DMG per second to ALL nearby enemy champions? even during a teamfight that is quite a bit, i would suggest making it something that interacts with his abilities in some way.
Q: Although the idea is good, JUST a small armor and MR boost isnt very unique, nor that useful, IMO a waste of an ability slot.
W: Tenacity CANNOT go above 35%, even Garen's W maxes at 30%, so trading AD AND AP for a stat that has a low max is pretty worthless.
E: This would be a GREAT ultimate for this guys theme, just up the DPS a little bit and make it an auto cast on the knock up thing, and it should replace his current ultimate.
R:Lower the DPS a great bit and SLIGHTLY lower the slow, and add a different effect, such as a dual effect on both cast types, and it should replace his E.
That is all i have to say, good luck! Also, please check out MY champ if you have the time