(Source)

In the comic "Friendship is Magic" by mauroz (You can start reading this here) a special group is slowly being put together under the command of Luna that works undercover completing several missions. According to the artist they will occasionally bump into the elements of Harmony.

Backstory(as explained by mauroz [with a few edits]):
The Elements of Sin are jewels like the ones of Harmony (although not as ancient), they where created in Equestria with bad intentions using dark emotions such as hatred and even love. They originally weren't named after the Seven Sins, but someone with great power brought them together and named as such to combat the Elements of Harmony. However, back in Equestria they did not have enough power to stand up to the Elements because there were more positive emotions in Equestria such as love and friendship. But now in the human world where there's a lot more negative emotions, their power has increased just enough to combat the elements of Harmony.

Members(as explained by mauroz [with a few edits]):
In the order they joined the group(some names haven't been revealed):

Lust: The Green-Eyed Guy:
He's been in the group the longest (and could be considered the leader), him and Luna are the only ones that actually know the creator of this group. He's manipulative and his actions aren't very clear, even his companions don't know his real intentions. However, one thing about him is certain: he never lies, since, for him, lying is the synonym of weakness. He has an odd obsession with Rarity and Spike, but his motives for the two are unknown...

Wrath: Luna:
Her past is the darkest of all of the members in this group, she was born in India on the night of Red Moon, her mother died soon after giving birth to her and she lived in an orphanages. As a child, she knew she was different because her powers awoke when she was little. The creator of this group found and recruited her and filled her head with numerous lies, eventually she realized she was being used and decided to defect. As a result, the jewel of wrath (currently)has no carrier...

Envy: The Blue-Eyed Guy:
He disappeared soon after Luna left the group. It could be said that he is the second in command. Unlike the beware of the Lust element, he has his motives clear: follow his creator's orders. Aside from his missions, he has certain interest in Applejack, but not even he himself knows why...

Gluttony: Gilda:
Her Element mirrors her hunger for victory. A disagreement with Rainbow caused her to break off their friendship; after it happens the element of Lust finds her and makes her one of them. Her intentions are just being the best and being with her friend again, whether Rainbow likes it or not (under the Element's influence friendship is not important to her, she sees it as only a trophy).

Pride: Trixie:
She's the daughter of a family of magicians (illusionists), but when she was a little girl she saw her parents being attacked by a bear during a vacation trip. She hid and saved herself, after that she was found by the FlimFlam bros. (the owners of a carnival) who were casually passing the town nearby. At some point in the past she suffered a great humiliation because of Twilight and was kicked out of the carnival and then found by the Lust bearer who promised her fame, love and a family if she joined the group. She wishes to prove that her magic is superior to Twilight's (side note: the jewel of Pride that she bears was, in Equestria, part of the Alicorn Amulet).

Sloth: The Hooded-One:
His only wish is to have fun (it doesn't matter if he causes disasters while doing it), he isn't interested in the group's goals actions, not even what the Lust bearer might be thinking. But if the missions are fun and he's allowed to do as he pleases, he'll support his leader. He also has a certain interest in Pinkie Pie (nothing romantic though).

Greed: Silhouette:
He's the most powerful of them all since he's the reincarnation of a creature that is said could defeat Alicorns (even Celestia and Luna). He is the most unruly and as such, the other members do not include him in their group. However the Lust bearer knows how important it is to have him. He is obsessed with one of the bearers of Harmony, who is, for him, an invaluable jewel...

4905278 I can't wait for these guys to make an appearance as the EoS. Judging from other works I've seen, Greed (the Silhouette) is Spike (after exposure to the Fire Ruby; Christopher was holding it at the end of Chapter 6 I believe).

4905287 My guess would be Tirek actually.

4928701 Meh. If it were, they'd probably have used a red or yellow highlight, not green.

4928701 Meh. If it were, they'd probably have used a red or yellow highlight, not green.