Miss Triangle (formerly known as "Miss Steinerflute") is a famous clothing designer who loves triangles. She is a triplet, and her real last name is Steinerflute. Her brother and sister are Brendan and Melissa, who are the butler and maid at Shapely Manor. The three of them teamed up to steal Lord Rectangle's birthday cake because their birthday was the same as his, which was always forgotten.
- She is based on the character Miss Scarlet from Clue.
- She has the same birthday as her siblings as well as Lord Rectangle, who always forgets that fact.