The Mabrigash are an Ashlander tribe settled in the Vale of the Ghost Snake, a swampland located to the east of Mournhold. They worship an entity known as the Ghost Snake. Despite being distrustful of outsiders, they are not openly hostile towards them.
The Mages Guild is an association dedicated to magical learning found all over Tamriel. To gain reputation with them, you must bring them lost tomes of Tamrielic lore. Each lorebook adds five points to the Mages Guild skill line, and an increasing number of points is required to gain a rank. Good relations with the guild can earn you new skills, perks, and abilities. The Mages Guild quest line is focused around the Daedric Prince of Madness, Sheogorath.
The Malacath Fanatics are a group of Orcs that invaded the Temple of Ire and took the priests of Trinimac hostage. They are secretly members of the Vosh Rakh, extremist Trinimac worshippers who hope to give Wrothgar's Malacath traditionalists a bad name.
The Maulborn are a secretive cult, mainly found in Deshaan. Although initially posing as a philanthropic group working to combat the Llodos plague, it soon comes to light that they are the ones spreading the disease in order to raise an army of plague husks. They are led by the mysterious Magistrix Vox, who seeks to return Morrowind to Daedric worship due to a personal vendetta against Almalexia.
The Midnight Union are a band of smugglers in Stormhaven. Despite being known for being on good terms with the Spirit Wardens, they attacked Pariah Abbey and stole a powerful artifact, the Dream Shard. This, along with other recent suspicious activities, raised doubts about the mental health of their leader, Count Hosni at-Tura, a nobleman of the Wayrest court.
The Morkul are a clan of Orcs who possess a stronghold in Wrothgar. A group of them has recently occupied Torog's Spite, a cave located near the city of Evermore, from where they intend to exact their revenge on the Bretons for the sacking of Orsinium.
The Moss-Skin Tribe is an Argonian tribe found within Murkmire. The tribesmen are mellow and inscrutable; often taking life as it comes and offering no resistance to the river's flow. They nurture the Hist, and the Hist nurtures them. They believe that if something happens, then that is how it's meant to be. When Sithis decides that things have become too ordinary, it disrupts the river's flow, and the Moss-Skins find a new routine until it's time to change again.
The Moss-Skin tribe is malleable to the flow of time, and very willing to enact change. They tend to appreciate impermanence, such as the stilts on reed-houses, which will eventually need to be rebuilt or replaced.