Vi's ultimate ability (Assault and Battery)

Vi and Malphite are both immune to all crowd control effects while their ultimate is active.

Like... all of them. For reals. Only the champion dying before they reach their target will stop the effect from going off. If Vi's target becomes invulnerable/untargetable (ex: Kayle Ult, Zhonya's, Fizz E, Vlad W) she will not damage/CC them, but will still unstoppably move to their location.

If the CC effect lasts long enough (ex: Morgana Q) Vi/Malphite will still be CCed after their ult animation completes.

Vi's ult will also fail if the target gets insanely far away (like if Teleport or Recall goes off right before she reaches them, or a global-range teleport like TF's or Rek'Sai's ult), but no regular movement ability can get you far enough away in time.

She's supposed to be unstoppable during her ult... She can't be cc'd at all, just damaged. That's the point of her ult.

You can kill a Vi during her ult, but only a few things interrupt it (such as going untargetable). She herself cannot be interrupted, however.

She's immune to all CC during her ult. If you want to avoid it, kill her before she reaches you, or become untargetable (Zhonya's, Fizz Trickster etc.)

from what i know bards ult can pause it but she continues to pursue who she targeted after the ult is over. but you can use zhonyas or banshees or anything that makes you invulnerable before the point of impact

"nope there's nothing to stop it, you are guaranteed to get dunked"

Fizz E too

Does Alistar's headbutt atleast work?

Best thing to do is move out of the way (so you don't get hit along the way to primary target) then cc her as soon as she lands. ...killing her mid-flight will also end it..but..that's usually not possible. There's a few unstoppable skills in the game- 's ulti's...forget if there are others.