Hahaha, great title. Like Beach, I've seen this happen a few times and yes, sudden exposure to sun is not good. I think this happens when you buy a plant grown by a grower who uses lower light and more fertilizer to grow plant big and fast. When you get it home and place it in higher light the sidewalls, which are usually protected in nature, become exposed and burn/dry out. I also think the new leaves adjust to higher light before they emerge and so will grow more compact, not high up enough to split the old leaves. Then we have a simple matter of following the path of least resistance. Do these plants make my butt look fat... you're so funny. Thanks for the laugh.

Hello, dahlialady! Welcome to the forum! Soil questions are heavy around here, for many reasons. Our differing climates, range of available materials and varying results over time make it almost impossible to say, "This is the mix that will work for you." I can just FEEL my friends hovering over this one like a day-old donut... I'll bite, since your bait is so delicious to me. Any succulent mix needs to be well draining. Every "Cactus Mix" I've tried has been too rich, not enough drainage, too much bark. Here's something it took me too long to figure out... bark is bad! It's still decomposing, too hot, roots don't like it. I don't even bother with cactus mix anymore. I'm going to give you my formula for mesemb mix which is a greenhouse mix intended for controlled use of water. I'll then explain the difference between that and my outdoor mix. You must keep in mind that I live in a very moderate part of southern CA. Nothing freezes here. I start with Miracle Grow moisture control mix... What???... I know! It blows my mind too! It turns out it just has a nice mixture of peat and forest products, light fert and other components too tricky to find and measure yourself. Plus, it's very nicely mixed/fluffed up and it has very little bark. I sift it at 1/4" to get the bigger chunks of bark out. This also makes sure all the peat is broken up. To this, I add: washed sand - about 1/3 the amount of potting soil vermiculite - about 1/4 the amount of sand The sand and vermiculite have their own qualities but what they do in a simple sense is cut down the ratio of organics/inorganics in your fines. All my fines are together now. I like to mix them very well at this stage, thoroughly amalgamated. I then add Perlite and Volcanic Pumice to equal about 1/2 of the entire mix. I use more Perlite than Pumice - 3 parts Perlite to 1 part Pumice or 75/25, maybe 70/30. Mix all that up and you have it! Plants that are grown in greenhouse conditions where they get plenty of light to transpire their water and watering is controlled, do very well with this mix. Outdoor plants, Indoor plants, or plants that have been accidentally overwatered do not do so well with this mix. It's still well draining but stays wet too long for shady or rainy conditions. Don't worry! I didn't make you read that for nothing! All it needs to become outdoor mix is more drainage which just means a bit more Perlite and Pumice. I would call it about 65% grit, 35% fines. There are other things people use for grit like turface "chicken grit", coarse vermiculite, scoria... you use what you can find. If anybody has any other thoughts on soil, feel free to jump in... I'm about done. I'm not going to jump on the defense if anyone disagrees so have at it :) I'm glad you found a Pleios 'Royal Flush', beautiful plant. If you haven't already, remove all of the old soil with the hose. Remove the fine hairlike roots. Don't be afraid, just pull them off with your fingernails, they will be damaged anyway. Let it dry out for a day and then pot it in the mesemb mix or something like it. Mesembs generally do not grow well in too gritty of a mix and they love sand. Put it outside but in the shade, maybe under a table, for about a week before you increase light. I usually use a couple stages of increased light over the next week until the plant is in it's final position. Mist on the 2nd or 3rd day after transplanting, give it a good watering on a hot day once you get it in the sun. Pleiospilos can take lots of light, growing nice and compact with good coloring. Not full sun but maybe 75%? Water when outer leaves are absorbed. Water when the inner leaves feel soft. Decrease watering when plant is splitting as it is consuming the outer leaves. They still need mist and a periodic drink, though... don't want to kill the roots. When the old leaves are obviously on their way out (you can tell they would not plump up again if you were to water) then you can give the roots a good drink, you will be itching to by then. Oh, man... I have stuff to do. Good luck!

Houseplantlover has the right idea, though I'll add a few things. Keep in mind that I'm also still a novice and in the end, Google is your friend. First, that picture is not what you should expect your lithops to look like. I think a few species do tend to "gape" like that, but most lithops will have their leaves close together. Google lithops and check out the images to see what most of them should look like. Also, the lithops on the right is overwatered. If probably kept, each head will only have one pair of fully grown leaves; this one looks like it's been watered over the winter. As a rule, do not water your lithops during the winter at all. I've read of some growers watering very shallowly on occasion, but these are experienced lithops people who know their plants well. Be careful about using sand. Fine-grained sand can actually make the soil more compact and keep it wet. Perlite should work well, though at two thirds I think it would float on top of the cactus mix. Maybe you could replace half with something like aquarium gravel of similar size. Just a suggestion, but you seem to have the right idea soil-wise, so whatever works and is available to you. Again, not a lithops expert, but good luck with your plants. It's pretty cool that first time a fresh new leaf pair emerges. Actually, it's still pretty cool the tenth time.

Is that the only lithops in the pot? I'm new to these babies too but that looks like it might be rot. Do you have suitable potting medium for them? And how's the humidity?