The Marshmallow Majorettes are a trio of one-time villains from the 2016 reboot of the Cartoon Network animated series The Powerpuff Girls, only appearing in the episode "Checkin' Out". They are three cheerleading marshmallows, who are mascots of their own eponymous brand of cereal. Bubbles imagined them as friends, who turned into enemies in a fit of petty jealousy.
Bubbles went to the grocery store to buy some cereal. Blossom told her that she could only choose one cereal and it was very important that she chose the right one. While looking through all the options, Bubbles had a lot of trouble making the right decision. It also did not help that the fate of the world rested in her hands, what with the Hungry Alien planning to destroy them if he did not get his delicious dinner.
While pondering which cereal box to choose, Bubbles started imagining all of the cereal mascots coming to life. One of the cereal mascots was The Marshmallow Majorettes of the eponymous brand of cereal. The Marshmallow Majorettes jumped out of their box and did a little cheer for Bubbles, saying that they would help her save the world. Bubbles had lots of fun, making her decision, once she began partying with all of the cereal mascots and having a great time, making friends with them.
Eventually, after enough partying, Bubbles had to make a decision and it was not easy, given how much the other cereal mascots were pressuring her to do so. "Pick me! Pick me!", they all said, to no avail. Bubbles still couldn't make up her mind. "Choose all of us!" they offered, but Bubbles sadly told them that Blossom only allowed her to choose one. Every cereal mascot went right back to begging "Pick me! Pick me!"
Bubbles finally chose Cherry Chimpanzee, which angered every other mascot. In an awkward and instant shift of tone, every mascot turned on her and chastised her for not picking them. The Marshmallow Majorettes were very pissed off at Bubbles for not choosing them, especially after they had done so much dancing and singing for her.
The Marshmallow Majorettes, along with all the other cereal mascots cornered Bubbles and prepared to attack her but Cherry Chimpanzee showed Bubbles a hose, that sprayed out milk. Bubbles used the milk hose to blast all of the cereal mascots. Upon being squirted with milk, all of the cereal mascots melted to oblivion.
However, this was all happening in Bubbles' imagination. In real life, she just took a bunch of milk and started dumping it all over the cereal boxes, which led to her getting promptly kicked out, without any cereal at all.