First of all, the tooltip should say 25% -> 30% attack speed, but instead, it says 5 -> 5.
Secondly, it's not protecting as it should. An example I go through Bard's portal, upon exiting the portal I cast shroud. Bard then casts his Q, and I still get stunned.
It's a feature, you'll block the 1st part of the spell that deals damage and then the 2nd part of the spell that applies cc upon it hitting the wall will activate. There's a few multi component spells that work like that vs spell shields.
Was the bard's Q hitting before hitting the wall? If so, then it is similar to Sivir trying to spell shield Zed's ultimate's damage. It does not work, because it is already on you (though Zilean bomb is kinda funky, it does stop the bomb damage).
Oof, I just made a thread about Nocturne's W lol. Only the AS part, as the others stated, the bard stun thing is intended
