The Master of Whistles is a teapot with mastery over whistling. She resides in the Mystical Mounds of Gomera and is willing to teach those who wish to learn her secrets.
Due to not being able to whistle after receiving help from his friends, Robin traveled to the Mystical Mounds of Gomera to seek training with the Master of Whistles. She greeted him at the entrance and offered him a drink, but Robin, haven't realized her identity, told her that he couldn't be bothered with teapots. Insulted by Robin's insolence, the Master of Whistles whistled harshly, shooting Robin into the doorway. He recognized her as the master and knelt before her and told her of his wish to be able to whistle like her. She claimed that he would be able to do so and offered him the drink again. After he took a sip, Robin gagged and asked what the drink was. She calmly informed him that it was hot sauce and, after he whistled to blow out the steam, explained that it unblocked his doubt to prepare him for the training.
Throughout Robin's training, the Master of Whistles observed him. She whistled rocks to him and laid on his back when he performed push-ups. She also demonstrated how to use whistling to create fists to break wooden boards. When Robin blew back a rock at her, she merely smiled at his progress. At one point, Robin received an alert from his communicator that informed him that his friends were captured by the H.I.V.E. Five and he decided to abandon his training and rescue them. The Master of Whistles stood in his way and told him he wasn't ready before she whistled a fist, but it was stopped by Robin's fist. She immediately relented and told him to rescue his friends.
When Robin was worried of losing a battle with Gizmo's death laser, Robin had a vision of the Master of Whistles telling him to use his steam which allowed him to shoot the laser and Gizmo out of H.I.V.E. Tower.
The Master of Whistles acts like a patient and stern mother when training her students. When training Robin, she was confident that he could learn how to whistle like her and was never shown to be annoyed or bothered by his failure and only smiled in approval when he managed to shoot a rock back towards her. She is also very serious as demonstrated when she didn't laugh at Robin's pun. The Master of Whistles doesn't like when she is made fun of for being a teapot and would react by using her steam to blast Robin through the doors. She also showed signs of cowardice as she immediately changed her mind when Robin managed to stop her attack and told him to rescue his friends.
Through the use of her whistling, the Master of Whistles was able to perform many actions. She was able to summon enough steam to knock Robin backwards when he insulted her and demonstrated the ability to levitate by whistling. She is also able to blow rocks across surfaces or through the air as projectiles. Her most powerful attack is creating whistles to appear as a fist which she used to break wooden boards.