Mjoll the Lioness

Mjoll the Lioness is a female Nord in The Elder Scrolls V: Skyrim. She has traveled the world extensively and claims to be as experienced and well traveled as one can be. However, in one of her most recent endeavors she was nearly killed by a Dwarven Centurion in the ruins she was exploring. It was only by her skill and persistence that she was able to escape. Barely alive, she was saved by Aerin who then brought her back to Riften and nursed her back to health. While she recovered, he revealed to her the corruption that plagued Riften. To return the favor, she has sworn to do whatever it takes to rid Riften of the criminals and misers. To her disappointment, progress in that regard is slow. The city has to want to save itself before she can save it.

Mjoll is a kindly, though intimidating, person. She gains the most pleasure simply by doing the right thing and earning people's trust rather than by earning any material reward. She and Aerin may be found in the Bee and Barb inn or wandering around the city.

Interactions
When the Dragonborn first meets her in Riften, she talks about how she tires of the Thieves Guild and the other forms of corruption plaguing the city such as the Black-Briar family. She will also talk about how she came to Riften and how she lost her sword Grimsever while exploring Mzinchaleft.

To receive Mjoll's quest you must be at least level 14 and Mjoll must like you. The easiest way to gain her favor is to simply agree with her that the The Thieves Guild in Riften is evil. Alternatively, you can gain her favor by doing four quests for the various residents of Riften. Other players have reported gaining her favor by simply allowing three game days to pass after talking to her, but this is unconfirmed.

Her task becomes available as a conversation option once the conditions are met. Note that the Radiant Quest System only updates quest availability when certain events occur such as leveling up. PC users will find that using the console to set the player's level to 14 will not trigger the update. At a minimum, you must legitimately transition from level 13 to 14 for the conversation option to appear. It is also unclear at this time if other factors such as the number of unfinished quests may affect when and if the quest is enabled.

After successfully completing the quest, she can be asked to join you as a follower.

If you go to Mzinchaleft before activating the quest, Grimsever may be replaced with a hide shield. There is an unconfirmed bug regarding this scenario where the sword does not always properly spawn when returning to the ruin for Mjoll. Console players who encounter this bug will not be able to complete the quest without reloading an older game save. PC users that run into this situation may still make Mjoll a follower by using the console command: "player.setrelationshiprank 00019DF7 4". This is also a quick option for PC users who wish to make Mjoll a follower without fulfilling her requirements.

Mjoll may be recruited for the Blades, but Aerin will follow her to Sky Haven Temple. When engaging in a battle with a dragon alongside the blades, Aerin will follow and attempt to slay the dragon with his dagger. This usually results in his death.

Mjoll has been reported to kill NPCs over gear dropped on the ground, e.g. a belted tunic.

Marriage
If equipped with the Amulet of Mara, the player may have the option to marry Mjoll. The player must also have completed her personal quest. She can be both a follower and a spouse simultaneously. When married, Mjoll opens a shop and gives the player a profit of 100 Septims each day; everyday that you don't collect from her, it adds up.

Even when wedded with the player however, Aerin may sometimes continue following her. One solution to this particular bug is to kill Aerin. Alternatively, one may change followers for a time and then recruit Mjoll again, which may also resolve the issue. Methods of killing Aerin without upsetting Mjoll are as follows:
 * The easiest way of killing Aerin when Mjoll is a companion begins by telling Mjoll to wait inside a hold that is not Riften. Aerin will leave the hold and head back to Riften. He can be killed on the way back with no witnesses and without Mjoll hating you.
 * On PC, instead of directly killing him, you can open the console, select Aerin, use the console command "disable" to make him disappear.
 * One other way is to kill Aerin when Mjoll is a companion and is following you. Followers are oblivious to crimes. (confirmed, )

Glitches

 * If you buy her armor (which is the banded iron armor set) she will walk around in her underwear after you leave your or her house.
 * If you marry Mjoll she will not equip any rings. Possibly the wedding ring registers as worn even when you take it from her. (Confirmed Xbox)
 * While this holds true most of the time. She sometimes will equip rings you give her, but only after zoning, never right away.
 * When married to Mjoll, if you turn into a werewolf and attack her then turn back into a human she will still attack you and cannot be downed in combat. The only way to reverse this glitch is to save, and then reload your save.
 * Sometimes with the while the Blades quest "Dragon Hunting" is active, she is one of the Blades. If you remain AFK for too long, she may simply leave your service, and run back to the appointed dragon location.