Those leaves looks really water logged; any succulent needs to be in well draining mix, and receive as much light as possible.

If the roots and/or stem is rotted, rot will spread up the stalk very fast. It would help if you get it out of the wet soil, get all of it off the roots and see if there are any, and what condition they are in. The stem looks still green, but also check to make sure it is not soft/mushy.

Pls. indicate your general location to get better answers...(it would be best to post it next to your name).

Looks like Black Knight to me. Black Prince doesn't have the green coloration I don't believe

Nicholas

IIRC, Black Knight has pointy, more slender leaves than Black Prince. And Black Prince is little more common too....

This is Black Prince in full sun:

and in much less sun-indoors:

Thanks for the info Rina, I didn't know Black Prince could do that. I always thought with less light it'd just get leggy but still be 'black'. I'm still learning too :)

Thanks for the responses! I replanted the little guy in a slightly larger pot and put it in a warmer window with more sunlight, the only one in the house it could sit in safely. I'll see how it does after a little time there.

Was the soil waterlogged? Did the roots & stem seem ok(no squish, no bad smell)?

The soil was only moist at that point, there wasn't much soil to begin with. But the plant was root bound in that pot. Now that it's in a slightly larger pot with sandy soil the off colored leaves that are left are drying and the firmness is coming back to the others. I'm going to keep watching it to see if anything changes.

What kind of sand did you use? - it is generally too fine to be used for well draining mix.

It was cactus potting mix. It was labeled on the package that it was for use with succulents and cacti