Can Ezreal's Q crit with Statikk Shiv?
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http://na.leagueoflegends.com/en/news/game-updates/patch/patch-42-notes#patch-Statikk-Shiv
Statikk Shiv PASSIVE CRIT :: Passive now only critically strikes when the associated attack critically strikes
Since Ezreal's Q can't crit, Statikk Shiv's passive won't crit.
crit is not an on-hit effect like red buff and sheen. rather, it is an auto attack modifier. you have to actually auto attack to crit.
I believe so, considering GP can apply it with parrrley
No.
Crit isn't an on-hit effect, Mystic shot doesn't critically strike, you need to critically strike to electrocute things with Shiv.
"Parrrley can crit and applies on hit effects as if a melee basic attack."
You'll notice Parrrley's tooltip makes a deliberate distinction between crit and on-hit effects, they are separate things.
Also, Riot patched out all the unintended interactions with things that shouldn't critically strike, critically striking, more than 2 years ago now. Stuff like the bonus damage on Garen's silence or Xin'Zhao's knockup wasn't supposed to crit and used to initially, as did Ezreal's Mystic Shot under rare circumstances.