Ok... So the masque runs up and casts Dance of Caging on the superheavy.
Superheavy gets no save or Deny the Witch or anything and can now only move d3".
The Dance is not a shooting attack, so the masque can still run (and it's slaanesh, so it runs an average of 7.5"), to try to hide behind a rock or something, only to pop out again and Dance of Caging next turn again.
If you get the right terrain, maybe this lets you "box" a superheavy for a while so that you can position your units behind some tall buildings from it?