Before Season 1
When the concept of illusion came into existence, Trixx came into existence. Before the Miraculous jewels were created, Trixx and the other kwamis traveled all over the universe unable to interact with humans. Then, thousands of years ago, a mage created the Miraculouses. Trixx started out in China, and later in Germany. When her Miraculous was not being worn, Trixx was dormant in the Fox Miraculous, which was stored inside Wang Fu's Miraculous jewelry box.
In the first season, Trixx laid dormant in the Fox Miraculous.
In "Sapotis," Trixx came out of the Fox Miraculous when it was temporarily given to Alya by Ladybug. She was impressed by her wielder's observations and transformed Alya into Rena Rouge. With help from her Miraculous' power of illusion, Ladybug, Cat Noir, and Rena Rouge defeated the Sapotis and returned Alya's sisters to normal. With the mission over, when she noticed that Alya was hesitant to return the Fox Miraculous, she agreed that they made a great team but also reminded Alya of her heroic qualities, including trustworthiness. Alya gave back the Fox Miraculous to Ladybug with Trixx dormant in it again, and Marinette returned it to Wang Fu.
In "Syren", Trixx transformed Alya into Rena Rouge and assisted Ladybug and Cat Noir with catching a pair of runaway panthers. Afterwards, Trixx returned to the Fox Miraculous and it was returned to Wang yet again.
In "Sandboy", Trixx was celebrating Nooroo's birthday in the Miraculous Box with the others kwamis and was excited when Tikki and Plagg arrived. The kwami marveled at the gift Tikki brought and though it was a paintbrush and played with the other kwamis. When it came the time to find Nooroo, Trixx and the others got into position but in an effort to contact him they contacted his wielder instead. Hearing his voice made her shutter at the thought of being his slave and to prevent being discovered they all cut off the connection. But realized if they contacted Nooroo's wielder then someone must have been akumatized and the danger Tikki's and Plagg's wielders are in.
During "Catalyst", when Scarlet Moth unleashed an army of akumatized villains on the city, Trixx and her Miraculous were retrieved by Ladybug which was then given to Alya. Upon briefly meeting Nino, Trixx informed him that superheroes must keep their identities a secret before Alya transforming into Rena Rouge.
In "Miraculer", Trixx was once again given to Alya by Ladybug to help her and Cat Noir fight Destroyer. Once the villain was defeated, she was returned to Master Fu. Trixx's Miraculous was subsequently loaned out again when Sabrina was akumatized into Miraculer and Mayura entered the fray. With the whole team, they were able to defeat Miraculer and stop Mayura from taking Bee Miraculous. Afterwards, Trixx was returned to Master Fu again.
In "Kwamibuster", he was activated along with his kwami brothers and sisters to help Multimouse enact her plan of rescuing Tikki and Plagg. By fusing his powers with a Multimouse clone they became Multifox. During the confrontation, Trixx was one of the few kwamis to avoid capture. After Kwamibuster's defeat and ending the illusion, Trixx and others cheered for Marinette as their plan was a success and was returned to Miracle Box.
In "Miracle Queen", Trixx was activated by a possessed Alya transforming her into Rena Rouge and his powers were used against the heroes until they managed to deakumatize the titular villain. After Hawk Moth and Mayura fled and the role of guardian was passed to Ladybug, Trixx and his Miraculous were retrieved and placed in the Miracle Box.