Riot tried too hard to push Vayne into the spotlight.
5 Buffs/'Bug Fixes'/QoL Changes in 8 Patches.
V6.22 Final Hour Stealth reclassified as Invisibility.
V6.20 Tumble BUG FIX: Fixed a few spots where Tumble was able to move across ledges.
V6.17 Tumble Bonus damage increased to 30 / 40 / 50 / 60 / 70% AD from 30 / 35 / 40 / 45 / 50% AD.
V6.16 Tumble BUG FIX: Now properly damages inhibitors and the nexus.
V6.15 Tumble NEW EFFECT: Can now be used on turrets. BUG FIX: Fixed a bug where Tumble's bonus damage was using an independent crit roll instead of being tied to the same crit roll as Vayne's basic attack.
The Bug Fix in V6.15 and the Buff to Q in V6.17 are particularly noteworthy changes. I'd say it's a classic case of pick one, not both. If I had any say in the matter I'd stop Vayne's Q from critting full-stop - she's primarily been an AD-Lifesteal-Attack Speed champion since BotRK got reworked years ago. Burst Build/Crit Build Vayne is simply exacerbating an issue that's been lying dormant in her kit since release.
