Mordekaiser uses his ultimate onto Lee Sin which was the champion Yuumi was bound to. As Mordekaiser takes Lee Sin to the death realm, Yuumi is sent out of Lee Sin. The Vi uses Vault Breaker (Q) to attack the Yuumi but it passes through the champion. Did not test this to see how frequent this may occur.
_Theory: _ Even though the Mordekaiser takes Yuumi out of Lee Sin, she is still considered untargetable for some reason?
1. Bind Yuumi to a champion.
2. Mord ults champion Yuumi is bound to.
3. As Yuumi is sent out of the champion she is bound to, Vi tries to Vault Breaker the Yuumi.