The Smooze is a slime creature who first appears in the season five episode Make New Friends but Keep Discord. He is Discord's friend and guest to the Grand Galloping Gala. Though Discord mentions that the Smooze is genderless, he is often addressed with male pronouns.
In season 5 of FiM, a new version of the Smooze appears in the episode, Make New Friends, but Keep Discord. This version of the Smooze is completely different from the one in the original, it is now a green, smiling blob like creature that gets bigger every time it eats something shiny.
When Discord decides to show up to the Grand Galloping Galla, he decides to bring the Smooze as his plus 1 in order to show up Fluttershy's new friend, Tree Hugger. When they get to the Galla, everyone is immediately disgusted upon seeing the Smooze, as he slides around the floor, leaving a trail of slime, and Twilight warns Discord to keep his friend under control. Discord introduces the Smooze to Fluttershy and Tree Hugger, trying to get the attention of Fluttershy and push Tree Hugger away to no avail before neglectfully locking the Smooze outside.
While outside, the Smooze begins to devour the other guest's jewelry and proceeds to grow, angering Twilight and the other guests. When Twilight reminds Discord of what she told him, he states that he "has better things to do than watch that thing all night", only to jump to control his guest when he realizes Fluttershy most likely heard what he said.
He then locks the Smooze in a closet, stating that he will let him out after the Gala is over, not realizing that he locked the Smooze in a closet full of gold and jewels. As Discord is giving a terrible stand-up comedy performance, desperate to make Fluttershy laugh, the Smooze bursts out of the closet, giant sized, and cover the entire room in his slime, unintentionally disabling Princess Celestia's magic.
Tree Hugger then uses calming noises to make the Smooze reform it's self, stating that a gelatinous creature like the Smooze only reacts to vibrations. With Tree Hugger becoming more popular than ever, Discord becomes enraged and tries to banish her into another dimension, preventing Twilight, Rainbow Dash, Applejack, Rarity and Pinkie Pie from stopping him by throwing a disco ball past them, which the Smooze goes after, absorbing them in the process. After he realizes why Fluttershy brought Tree Hugger and the errors of his ways, Discord removes all of the Smooze's shiny objects and apologizes for neglecting him. Smooze and Pinkie Pie then dance on the dance floor.