I was playing Master Yi. I had boots, phantom dancer, static shiv, and movement speed quints. My question is how was Vayne faster than me even during my ult?
Vayne's ult gives her a ton of MS when chasing someone and the CD on Tumble is nearly instant if Vayne manages to make use of the AA boost right after tumbling.
She can reliably catch pretty much everyone trying to run away from her, be they Nidalee, Riven, Udyr, Master Yi, Singed, or anyone else with impressive endurance-race capabilities.
Also: Movement Speed that isn't from boots if found almost exclusivly on attack speed items, and Vayne's kit allows her to build pretty much nothing but attack speed items. I'm pretty sure her ultimate and passive also grant her the same type of flat movement speed as boots that %MS items actually use for more bonuses.
Anyways: running away from Vayne is generally a bad idea. It causes her to take 0 damages when she gets to shoot you in the back for free.