Vayne just did an enormous amount of damage in a very little amount of time.
So let's calculate: Auto ~ 600 Crit Damage +8% current health> Tumble + Auto + Crit + 8% current health ~ 950 Dmg > Silver Bolts + Auto Crit + 8% Current Health ~ 1,000 Damage > Bork Active 250 Magic Damage > Tumble + Auto + Crit + 8% Current Health ~ 950 Damage.
Why can vayne do this much damage in just a few autos and all within a few seconds while jumping around everywhere and going invisible? Not to mention that she gets a movement speed buff when running towards enemies.