Stench is a mutation found in a poisonous pipe in the sewers. It allows you to excrete a musk that makes NPCs less likely to attack you, but it makes you easier to track.
Stench is located in the poisonous pipe in the South East of the main part of the Sewers. Because the poisonous pipe is, well... poisonous, it's highly recommended (read: necessary unless you want to die) to wear a gas mask when you are getting the mutation. A belt light, or some other light source, is also recommended unless you can see in the dark, and you need to be able to stave off the chuds and chobos that like to lurk in the sewers, or at least have a friend willing to save you from them.
Stench gives you the new command 'musk'. While musking, you release a horrible-smelling odor that makes most NPCs less likely to attack you. You also receive +2 endurance, as well as -2 senses and cool, whilst musking.
Additionally, you become significantly easier to track while musking, and moderately easier to track while not musking.
Lets you get past areas without aggroing all those pesky creatures that slow you down, and makes it less likely you'll get one-hitted by that grue you didn't see. Also, the minor endurance boost is always nice for more smashy-smashy characters.
People have an easier time finding you, but you have a harder time finding them. Also, now you smell funny.
The -2 cool and senses whilst musking further hurts persuade (-1), fuck (-4), and track (-2).
S/he smells HORRIBLE, like cheese left in the sun.