Udyr's Bear Stance doesn't trigger Sudden Impact

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Udyr's bear stance does not have a dash it has a speed bonus. just go ravenous hunter on him and never use w because your q now does better healing and damage.

... I'm not sure if you think I'm stupid, or what. I know his Bear Stance's primary effect is bonus movement speed for a few seconds. However, similar to Ekko's Phase Dive or Rengar's Innate, your first attack in bear stance against a champion causes you to lunge ~100 units closer to your target. It was literally in the patch notes when they added it, and it's still functional in-game. Trundle's Q also does this.

http://forums.na.leagueoflegends.com/board/showthread.php?t=3268405 Udyr now performs a slight dash when stunning an opponent.

https://na.leagueoflegends.com/en/news/game-updates/game-updates/patch-36-notes Dash now only occurs versus champions.

And it's still active in-game, even after 4 years.

https://www.youtube.com/watch?v=kkEg6Z0h8ps

And it's completely irrelevant whether or not the mastery would even be good on him - this is the bug reports forum, and there is a bug.

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If that were the case Trundle's Q would also have to apply it since it does lunge towards your target in such a way.

Well yes, but I haven't tested Trundle.