That does look like rot. The only solution here would be to cut above the withered portion to clean flesh, then root. Remember not to water until you see new roots.

How is your soil? Approximately how much perlite is in there?

Yeah definitely looks like Rot. Had this happen to mine too. How often did you water it?

Sometimes plants you buy were already over watered at the nursery, so there's nothing you can do. Best is to always check the roots after you get home and repot to a better soil. .

The transplants are a couple of months old but the bottom picture is actually a hobbit variety we've had for a year or two. It got sunburned last summer but I repotted it a few months ago with new soil and started acclimating it to the sun and it was doing perfectly well - putting up new shoots, dark green, and everything. As far as the soil, it's 3 parts potting mix (the miracle gro one for cacti/african violets), 2 parts coarse sand, and 1 part perlite.

I broke off a leaf from the hobbit to cure and propagate but would it be ok to cut off all of that rot? That would leave the entire "leaf" part without any roots :( I don't mind the new transplants so much since the mother jade that I took them off of is doing ok but the hobbit I'd love to save.

Yes that's the only way to save it, otherwise the Rot will speed further up the plant and eventually everything will be rotting within week. And to know the difference between Rot or under watering, because both have a lot of similarities, is that Rot spread super fast, within a few days drastic changes occur, just in your case. Where as overwatering is much slower.

Don't worry about cutting the roots off. Succulents and cacti are very opportunistic growers, that's why just plucking a leaf you can get roots and a new plant. Just cut it somewhere further up the Rot to make sure absolutely no Rot is left on the stem. Let it callous over for a few days and you can plop it back in the soil.

Then, it is very important to not to water it when there are no roots. Its pointless since with out roots it can't absorb water. So best leave it be, and when you start seeing new growth you start watering. New growth means roots have established.

The pots also need to be filled more than at present, so that the plants are set higher in the pots in relation to the rim. At best, the soil line should be half way above above the 'stepped' part of the pot. Setting them too low can create shade and extra humidity which won't help if you are getting issues such as this :-) This applies to any plant, not just succs.

You can grow plants in any 'soil' you wish, but need to make sure that it doesn't stay too wet for too long. Btw, no watering or watering in sips is not the answer...Plants should be watered thoroughly when mix deep inside of pot is just about completely dry. Checking just the surface or near the top of soil isn't giving proper picture.

Plants that can't support themselves (even trailing plants should have sturdy stems) are often etiolated (weak, skinny stems). More often there is damage to roots (dead or rotted) or roots may not be established if new cutting or transplant. Stems could be rotting (very often) and can't support plant. If sticks or other ways of support need to be used (except if a cutting or very recent transplant) - there is some kind of a problem and should be solved.

Many ppl use 50/50 soil/coarse perlite mix. Many use much more gritty and mostly inorganic mix.

How coarse is your sand? It shouldn't be finer than what stays inside of sieve if sifted. IMO, you are using too much soil (and preferably no sand if fine).

Rotted stems and/or leaves are, most often, also soft and maybe even mushy. They are also quite dark in color.