Kassadin's W doesn't apply when hitting a tower.

Activating 's W, Nether blade, doesn't allow Kassadin's next auto attack to deal extra damage to an enemy turret. His W will, however, still enhance his next auto-attack on any other non-turret enemy. If this is intended, then the tooltip needs to be changed to specify that this doesn't apply to towers. As is, however, it states that his next auto-attack deals extra damage. No exclusions are made.