When moving a unit with Showstopper (or Leona's spell), can other units from the base join the same attack, or must the moved unit attack alone?

Ruling: When you move a unit with a spell like Showstopper or Leona's spell, you cannot move other units alongside it - the unit must attack alone.

Nuances:

• You can only move multiple units together using the standard move option, not when moving via spells