From the Super Mario Wiki
Diva's Lips is an enemy in Wario Land 4. It appears exclusively in the final battle against the Golden Diva. At the battle's beginning, Princess Shokora, who has been transformed into a Black Cat, gets swallowed by the Golden Diva. Wario is left to battle by himself. During the battle, when Wario brings the Golden Diva to her last point of HP, she will be destroyed and all that will remain is her Lips wriggling helplessly across the stage. They can easily be defeated by a simple Smash Attack or Dash Attack. Once Wario destroys the Lips, Princess Shokora is freed and Wario gains victory in the battle.