If Vayne is even slightly fed early game
One of the worst early game ADCs shouldn't be getting fed early. Vayne shouldn't be able to get off her silver bolts in lane unless you all in her when she has full HP, Vayne should be able to be poked via abilities/AAs without being in range to retaliate during lane.
she turns into a monster that can pretty much one shot anyone on the team.
3 shot. It takes gettingher bolts off to kill someone because she builds more AS than AD/Crit.
much one shot anyone
Armor and not Armor + massive HP is your friend. her bolts do percent hp so something like randuins/sunfire against her is less effective.