This has been confirmed by Riot to be a bug, and it will be fixed in an upcoming patch.
Source:
just tested a fix for this—going to try to get it into the next
release. looks like powerchord was set up to deal damage to inhibitors
and the nexus (which is why it was consumed) but a bug was preventing
it from being applied. we're just going to fix the bug, so sona will
be able to powerchord inhibitors (and the nexus) when that goes out.
you can't diminuendo or slow structures though, so be mindful of that
if you're going to use your passive for extra damage.
I'm just theorycrafting here. Say the Tumble animation takes 0.5 second. The Attack Speed stands for the number of attacks fired per second. I'm also presuming the Tumble is executed perfectly after firing a shot to minimalise 'auto-attack-cooldown'.
Tumble will increase your next attack's damage with 30/35/40/45/50%. That would mean Tumble lets Vayne do 1.3/1.35/1.4/1.45/1.5 attack in one shot, in one half a second.
I'm gonna take a long fight into account, where Vayne has the time to Tumble twice. That would mean Vayne does 2.6/2.7/2.8/2.9/3 attacks in a second.
So, if we are taking in account that NO damage boosts are used, for example from Sheen's proc, then you'll need an Attack Speed of 2.6/2.7/2.8/2.9/3 depending on Tumble's level to match the damage output.
This is not calculating armor and armor penetration. That means the actual amount will pretty much always be lower. If you have Trinity Force, that amount will be considerly higher again. That item will net you another 0.5 on top of your shot per time, meaning the Attack Speed would have to be higher then 3.1/3.2/3.3/3.4/3.5. Again, this is actually lower because of the Armor stat.
Also, I'll repeat, I'm just theorycrafting and presuming perfect conditions and a Tumble duration of 0.5 seconds. But, the maximum Attack Speed is 2.5, which is actually met on the highest level of Tumble when Tumble would take a whole second. And I doubt you'll achieve the maximum Attack Speed in a game often. Then again, I'll repeat myself for the 3th time and tell you Armor will mess with the theory.
As a conclusion, I dare say you should dance around with Tumble to achieve maximum DPS, especially with helpfull items that proc spell casts.
Best Answer
Yes Runaan's work with her Q, the miniprojectiles from Runaan's all proc the AoE damage.
Notice in the test video that an explosion happens each minion hit by any of the projectiles. The AoE damage can also crit, near doubling her damage output.
Note from creator of the champion