One day at school last year, she and Chuck Clayton had a brief discussion in the library, Ethel assisted him with a math problem, and that was all. However, Chuck began to spread a rumor that he and Ethel engaged in sexual acts. Following that, someone wrote "sloppy seconds" on Ethel's locker.
Ethel joined forces with Betty Cooper and Veronica Lodge after learning that Betty was looking around school for female students who were also slut-shamed by Chuck Clayton and his posse. Ethel then volunteered to go on record with her story, she told them that after a short conversation with Chuck in the school's library, he went on to ruin her reputation by spreading rumors of him and her together. Betty sympathized with her, feeling bad that Ethel had to go through such an experience. But that's wasn't all, they also keep score of each conquest, which earns them a point, they keep all this hidden within a secret playbook, according to Ethel. And due to lack of evidence, Mr. Weatherbee's hands are tied, meaning that he would be of little help.
Upon learning from Trev Brown, the potential location of the playbook, Ethel, Betty, Veronica, Cheryl and Kevin Keller broke into the school after hours to recover it. In the book, Ethel was discouraged to learn that she is labeled as "big girl (7.5)". With the proof provided by the playbook, the ladies manage to take down Chuck and his goon squad. 
Several classmates were disturbed by Ethel's reading of an extremely dark poem, specifically Kevin and Veronica, which resulted in Veronica taking a personal interest. While Veronica was moved by Ethel's poem, she could also tell it was coming from some place dark, which led her to ask if Ethel was alright. Ethel admitted that everything was not okay within the Muggs household as her parents had been constantly fighting, but they would not tell her why. She felt as if something really bad was happening, and there was nothing she could do to stop it, like watching a slow-motion car crash. In an effort to cheer her up, Ethel was invited to lunch and pampering with Veronica and Kevin at the Pembrooke.
As promised, Ethel had lunch with Veronica, Kevin, Betty, and Hermione, however, due to all the stress she had been undergoing at home, Ethel wasn't feeling hungry. Her living situation hadn't gotten any better, as her parents were still fighting, and after some bad luck with their savings, they were going to have to sell the house. At that moment, Veronica realized that she and Ethel had more in common than she originally thought because the Lodges had also lost everything several months prior, but Veronica reminded Ethel that she still had her family and friends. Unbeknownst to either Ethel or Veronica at the time, Hiram Lodge, Veronica's father, was responsible for the Muggs' recent misfortune. So upon learning that Ethel's last name was Muggs, which the third "G" had been removed from when her grandfather came over, Hermione became fairly concerned.
The next day, Ethel was invited back over to the Pembrooke by Veronica, who gifted her with expensive clothing and jewelry, yet she didn't feel comfortable accepting them, Ethel only wanted to be friends. Just as life seemed to be getting better for Ethel, her father attempted to end his life after swallowing an entire bottle of pills. At the hospital, Ethel and her mother were greeted by Veronica and Betty, who came to extend their prayers to the family. After introducing Veronica to her mother, Mrs. Muggs discovered that her last name was Lodge, making her the daughter of Hiram Lodge, the man who was at fault for destroying the lives of the Muggs. Veronica then went on to apologize for her father's actions, which she could do something, but Ethel's mom wanted actions, not words.
The next day at school, as Ethel prepared for class, she was approached by Veronica, who was sorry for everything her family had done. Ethel explained to Veronica that she was not responsible for her father's actions, not to mention Veronica had been there for Ethel during her time of need multiple times. She then offered Veronica the desk next to her if she wanted it.
Jughead's Birthday Party
During lunch, Ethel was approached by Chuck, who was fresh off his suspension. Surprisingly, he came over to apologize, it would appear that his suspension offered him some time to reflect on his wrongdoings. Before long, Betty came over to the table and demanded that Chuck leave her alone, slamming her hand on the table in a fit of rage, but Ethel assured Betty that everything was fine.
The following night, Ethel attended Jughead's 16th Birthday Party, but before the party could even start, she found herself wondering if she could make it to the bathroom before Jughead and Betty returned from the double-feature at the Bijou, to which Kevin suggested that she holds it. Ethel peeked out the window to discover that Betty and Jughead were nearing the house, so she advised everyone to hide, and as Jughead entered, everyone jumped out. Then came the birthday cake, Ethel, Archie, Veronica, Kevin, and Joaquin surrounded Jughead as he blew out the candles.
Not long after the blowing out of the candles, the party was crashed by Chuck, Cheryl and the rest of the school, all looking to party. Later in the night, she offered Jughead a slice a cake as he passed through the kitchen, telling him that not eating his own cake on his birthday was bad luck. Unfortunately for Jughead, the entire night was bad luck. He denied Ethel's offer, and said he would see her at school.
When rumors about Midge and Moose's attempted murder spread at school, Ethel expressed her concern about a killer targeting students to a police officer sent to school to take some depositions. Ethel learned of Archie's Red Circle watch group, likely via flyers at school, and she didn't hesitate to call him when finding herself in danger. Walking home alone from school late in the evening, she noticed she was being followed by a van suspected of being driven by the Black Hood so she called Archie, who was riding with Reggie Mantle searching for him. Archie and Reggie arrived in time to save Ethel, who hid between some bushes while the mysterious driver went back and forth with his van looking for her before Archie and Reggie's arrival. She cried between Archie's arms, apologizing for not having recognized the driver, while Reggie tried to run after the van disappearing into the night.
Ethel approached Veronica in the cafeteria at school with a milkshake from Pop's and dumped it on her head. Ethel, along with others, had found Veronica guilty for the crimes that she and her parents had committed against the town.
A couple of days later, Ethel noticed Veronica's campaign for student body president, which involved bribing the male voters with kisses and cupcakes. However, as Ethel informed Veronica, she would have no such luck with those tactics in regards to the female voters. Veronica explained that she was only interested in one girl, that being Ethel. While it was long over due, Veronica wanted to make reparations. So she told Ethel to tell her father to expect a job offer very soon from her dad.
The next day, during Veronica's campaign rally, with information given to her by Josie, Ethel passed out flyers exposing Veronica for all her lies and wrongdoings. As for Veronica's half-hearted bribe with a job offer for Ethel's father, Ethel wasn't interested.
Ethel and Kevin sang "In" throughout the halls before running into the auditorium with Archie, Veronica, Betty, Cheryl, Toni, Josie, Midge and Moose. They got on stage, where they continued to sing and dance before being joined by Fangs, the assistant director. The cast then began introductions, starting with Archie who portrayed "Tommy Ross", the boy next door. Betty played "Sue Snell", the good girl. Veronica portrayed "Chris Hargensen", the mean girl. And Cheryl would be playing the iconic role of "Carrie White". As for who would be portraying, "Margaret White", Carrie's mom, that role went to Alice Cooper, which came as a surprise to almost everyone. Kevin explained that while her casting was untraditional, to him, there's nothing more amateur than age-inappropriate casting. Alice was both looking forward to playing Margaret and spending more time with Betty. Chuck Clayton joined them late after mistaking that rehearsal was in the music room.
Cheryl interrupted the rehearsal after hearing whisperings that some of them, mainly Ethel and Josie, didn't think she was fit to play the role of Carrie White. So to settle the matter, she began to sing "Carrie" to prove them wrong. After hearing Cheryl's performance, all doubts surrounding her casting were no more. Ethel, Josie, Veronica, Betty, Alice, Toni, Midge, Moose, Archie, Jughead, Kevin, Fangs, and Chuck gave Cheryl a round of applause. As Cheryl headed back to her seat, a heavy sandbag falls from above and nearly crushes her.
Ethel was Suspect #1 in Betty and Jughead's case to solve who wrote the letter pretending to be the Black Hood. In the student lounge, Betty tried to bait her. Betty accused Cheryl of always taking things she shouldn't, like the role of Carrie, to see if Ethel would agree. Jughead filmed from just outside the lounge as this unfolded. However, Ethel did not bash Cheryl, instead, she thanked Betty for the compliment of considering her to be a better fit for the lead role. Betty continued. For Kevin to cast Cheryl as Carrie without even letting Ethel audition, Betty wondered if that made Ethel angry. Ethel replied that she was born to play Carrie White. So to not be given a shot at it makes her angry. Unfortunately, Ethel noticed Jughead by the window and realized that she was being filmed and interrogated. She told them that she's not a violent person and that she would never harm anyone for her own benefit.
Ethel, Toni, Veronica, Betty and Chuck rehearsed in the auditorium, where they sang and performed "The World According to Chris". Everyone was highly impressed with Veronica as they applauded the routine. Betty credited Veronica's performance to her being the literal embodiment of Chris, the character she's portraying. Never had a role been so perfectly type-cast, Betty remarked.
Due to some unforeseen circumstances, Kevin informed Ethel, Toni, Archie, Veronica, Jughead, Fangs, Alice, Moose, Midge, Betty, Chuck, and Josie that Cheryl will no longer be playing Carrie. When they asked why, Kevin simply replied that Penelope Blossom wasn't much of a stage mom. In the meantime, Cheryl's understudy would assume the role, that being Midge, who Kevin appointed after the sandbag incident.
Opening night, in the dressing room, Ethel, Toni, Archie, Betty, Veronica, Kevin, Midge, Moose, Kevin, Alice, and Chuck sang "A Night We'll Never Forget". Afterward, she caught Jughead in her dressing room. Inside her dressing room, he found cut-out magazines, with letters missing, which Jughead surmised was used for the Black Hood's letters. Jughead concluded that Ethel was behind the threats as initially suspected, but Ethel ensured him that he had it all wrong. She cut the letters out the magazines for her vision board so she claimed before kicking him out.
The crowd was packed when the play began, and Alice started to sing "Evening Prayers". When Alice cued Midge, the curtains raised only to reveal that Midge had been murdered by the Black Hood. She had been stabbed with knives and scissors and pinned to the wall. On the wall, written in blood was a message. "I Am Back From The Dead. All Those Who Escaped Me Before Will Die... B.H" When Alice screamed in fear, the crowd realized that this was not part of the play and the auditorium erupted in panic and chaos.
The town gathers for Midge's funeral to pay respect. Cheryl sings a song in Midge's honor. She and the rest of the River Vixens are dressed in an all-black cheerleader uniform. Midge's death has seemingly taken a great toll on Riverdale, Mrs. Klump and Moose especially. Ethel stands alongside Mr. Weatherbee and the Blossoms as the service commences.
After learning about the letters from Jughead, the Sheriff turns his attention towards Ethel, who cries during interrogation. She admits that she was jealous as Cheryl often gets her way, but she never hurt anyone.
Ethel is a lovely young lady with pale skin, light ginger hair and brown eyes. She's a little on the heavier side, being labeled by the Riverdale Bulldogs as "big girl", but this does not take away from her beauty. Ethel has more of an unusual wardrobe, much different from that of anyone else in Riverdale. In most cases, she'll wear a blouse, paired with a thin sweater and a long skirt.
Ethel is a shy and quiet girl, the type to avoid problems and controversy. She keeps to herself and is heavily focused on school work. Beneath all that is a depressed and lonely young lady. The troubles that her family is currently facing certainly do not help. Despite her generally positive attitude, Ethel isn't afraid to get even. She is known to be quite underhanded and rude under the right circumstances, such as when she dumped a milkshake on Veronica, and later teamed up with Josie to ruin Veronica's chance of being school president.
Ethel is of Dutch descent on her father's side. Their family name was originally spelled "Mugggs" but lost the third "G" when Ethel's grandfather, Manfred Mugggs, immigrated to the United States.
Outside of Riverdale, Muggs is not a traditional "Dutch" surname, as the word, either spelled Muggs or Mugggs, has no meaning within the Netherlands. Mugg(s), however, is of English origin, originating from Somerset, England.
In the Archie Comics, Ethel is infatuated with Jughead to different degrees depending on the story.