Stuffcode potions, at first glance, appear as a non-descript potions with descriptors such as:

Once identified, you will find that they are actually one of the following:

More on mutations: (offlined Oct 2021)

All mutations affect your player body, so as long as you keep your body you keep your mutations. If you die and regenerate, you get a fresh body with no mutations. The one exception is if you don't log out as a ghost and walk to Frank's, you will get your old body back.

You can lose your mutations by drinking a potion of cure mutations. If you remain logged out for too long they also start to disappear. Remaining net-dead or logged in will maintain them.

Many of the beneficial mutations are percentage based, so as you get bigger they can be a significant boost. Many of the mutations stack, so cute is a small boost to CHR and very cute is a double boost to CHR.

Most races can get a max of 28 mutations. Drow elf can only get 27 because they already have darkvision. Races with tails can get 29. "very" counts as 2.

Here is a list of known beneficial mutations...

You uncork the bottle and drink the liquid.
You feel your body mutating.
You are now...

Here is a list of some known detrimental mutations...
(horns that prevent you from wearing a helmet, etc)

You stepped on a mutation trap!
You feel your body mutating.
You are now...

Unwanted mutations can be removed by getting a new body, or by drinking a potion of cure mutation. Also remaining logged out for a month should do it.