Here are the Sins!
Spoiler: Envy
Also known as jealousy by idiots, Envy isn't really jealous of anything other than... Well, a lot of things actually, but he doesn't do the spite thing very well at all. If the young Master picks envy, he slowly becomes a bit more bitter everyday, but in trade gets faster, develops sharp claws, has a thinner figure, and becomes more agile.
The owner of the Sin also slowly starts to mutate, becoming a bit more like the animal associated with the sin bit by but. In this case that animal is the snake, and thus the master will slowly get scales, have their eyes change into slits, and will be far more flexible than average.

Spoiler: Lust
Lust is a very attractive individual, and is in turn attracted to others. Very easily. Very, very easily. Lust also has a tendency towards flattering others, whether they want it or not, as his way of helping people. This has led to many unfortunate misunderstandings.
The powers Lust grants are: Enhanced Beauty, Charisma, and Lovecraft Tentacles whenever they're needed.
Strangely, the animal Lust is associated has shifted over the years to an octopi (I wonder why *Cough* hentai *cough*) so the mutation granted to the owner is now the gaining of tentacles and getting smoother, paler skin.

Spoiler: Wrath
Wrath is very... let's say protective. Wrath loves all of the young masters, maybe a little bit too much, and will do his best to protect them. Wrath has a very... let's say peculiar way of determining who is a threat to the master: If they hold a weapon, can cast magic that could harm the Master, or have anything that could be used against the Master, they need to be eliminated. The Master can usually tell him not to harm his friends, though.
The powers gained from Wrath are Super Strength, Size Growth, and a general increase in physical activity. However, those who use Wrath tend to become neurotic and paranoid.
Wraths animal is the Ox, so those who use him tend to gain Horns and Hooves. They also gain red skin. It is highly probable Wrath inspired the traditional thought of Demonic appearance.

Spoiler: Sloth
Sloth is very cowardly and timid, she dislike violence a lot. She tends to shy away as she believes she can't do anything right, and holds herself accountable for the deaths of every Master. Even if she wasn't the one in control. She gets depressed very easily.
The powers gained from Sloth are mostly Magic related: a sleeping Spell, and a Shield. Those who use Sloth slowly get more and more lethargic.
The animal most associated with Sloth is the Sloth, so those who use her slowly grow claws, get shaggier (though this may be because of being too lazy to shave) and get a little bit stronger.

Spoiler: Gluttony
Gluttony is a party kind of guy, who likes to make puns and crude jokes that everybody else hates (Pride secretly likes them, though). His response to everything is forget about it an go drink/eat/smoke away your problems, though is stuff gets serious he will get serious.
Gluttony's powers are Omnivorousness (i.e. you can eat anything.), and tounge manipulation. In turn the users addictions will be increased ten fold, and will mutate to be more and more toadlike.

Spoiler: Pride
Pride is very proud, not only of himself, but also of others. He believes everyone can become perfect, if they aren't already, and is a staunch believer in the thought that everybody is equal in their perfection. He can be somewhat oblivious to insults, though, as he couldn't understand why anybody would insult anybody else. He literally cannot understand sarcasm unless someone tells him they were being sarcastic.
This tends to get very annoying, very quick. His powers include getting a little bit better at everything, little by little, which may sound OP but by this mean you go up .001% every week. That you use that ability. He also makes people far more quickly self-confident, which can go to dangerous levels. He has no mutations.

Spoiler: Greed
Greed is the de facto leader of the Seven, and is very pragmatic. He has lead many businesses, including actively creating Venice as a pet project, and his idea of fun... differs from what we would consider to be so.
The powers gained from Avarice are: Increased Intellect, Increased Luck. He slowly mutates the person to be more Rat-Like, including glowing red eyes, a snout, and sharper incisors. The longer one uses Avarice the more they crave more things, be they Gold, Money, Fame, or Teapots (That was a very weird experience for the 7)

Please note that I will probably speed up mutations for RP purposes and fun and profit, so him using say, Wrath, will quickly make him demonlike and grow horns. Not HUGELY demon like, but pretty demonlike.