I'm with brad on this one, seems like the classic sunburnt. Plants are living things too, over exposure of high heat in prolong light can sorch leaves and effects are sadly permanent. Try to extend its sunlight exposure slowly by an hour more each week, and you have a good plant all set up there. Make sure you sterilize your tools well when you cut the declining inflorence (flower stalks), remember if your plant exposed wounds gets infected by pathogens or fungus spores - those unfortunate diseases kill plants very quickly with no cure to it. Lastly, I hope the "special soil" you bought aren't those commercial peat "cactus and succulent soil" from big box stores. Those are regular non-well draining soil marketed as fake cactus soil. You will need porous substrate such as a lot of perlite or pumice in your soil for healthy succulents. If you can master not overwatering your succulents, you have one fine plant looking good in weeks. good growing - bernard

So I got some cactus mix to replant it but unsure if the roots have rot or not? I'm not sure what makes them healthy or rotted. Another leaf has shriveled and was easily pulled off since yesterday. Would rot cause the leaves to shrivel? The top leaves are still healthy and growing but I'm concerned that with how fast they're dying the dead ones are quicker than the growing ones and it will all die. are its roots okay? edit: I take it back, while repotting it I lost 3 leaves, not just 1, and I can see another that's shriveled and still attached. I repotted it but if its roots are bad I'll go and redo it to get rid of bad roots. And what should be done for it after being repotted in terms of water and light? And will it be okay with the fact that as it's going to be next to my lizard tank to get the light from her tank, the light goes from dark to light very quick, unlike next to a window where it's gradual light changing all day? Her lights are on a timer so they go on and off at certain points of the day but once they're out it's totally dark. I don't want to shock the poor plant either

Oh boy this sucks;)! Euphorbia ingens are cold hardy down to about 28F. So from now on these will need to be protected during the coldest days and nights. I think you've learned that lesson;). Somebody should have made you aware of this when you purchased them. You live in a zone where the temps get down to 10F-15F so the seller should have least tried to sell you frost cloths at the time of purchase. I'm sure those Euphorbias were not cheap. This is tough a one because they're big and the pics aren't very clear. So it's hard to tell what's going on. The areas that look bad are they mushy? Regardless if they are mushy or not there is frost damage. The growth tip is destroyed. So those parts will no longer grow, but will branch on the sides:). So one of two things will happen or a little bit of both. The areas that have been damaged will either dry up like this. The above pic shows frost damage on my Euphorbia grandicornis from last winter. See how the damage just stopped and dried up. I probably will cut eventually. Or the damaged areas will get mushy and spread. Luckily your Euphorbias are on the bigger side so you can kind of wait and see. Keep a close eye on them. Watch for changes. I honestly wouldn't chop quite yet. Wait and see how things play out. If you notice things take a turn for the worse you will have to cut:(. E. ingens can take temps down to 28F, but for most of my plants I don't like to let them go as low as they can go. At least without some major protection. Any growth tips you see that don't have any damage cover with styrofoam cups or similar. This will help protect them. Heck I would even cover the damaged tips;). Then cover with the frost cloth. I know I didn't give that much advice, but this is exactly what I would do. I just think if you go and chop now it may be a little premature. I mean there is definitely damage, but I would just wait and see what the Euphorbias will do.

Agree with Matt, leaves look rotting but are also sunburned. Rot wasn't visible in other photos. Many of the leaves are sunburned toward the tips... I wouldn't worry much about looking for turface and/or bark unless they are easily found. I went thru all of that (as many others did); found turface but not too lucky with bark (lots available, but is too large - 2" and bigger). So I settled for mix I use, with ingredients I mentioned in previous post (including photo I posted). BTW, I have read all posts by Al. I am very strong 'believer' ...but if you understand principle, you can make excellent mix using materials easily available, without going crazy looking for exactly the same...For example: Al's recipe doesn't call for perlite. But knowing perlites water holding capacity, one can figure out what it is good for and use it as a substitute for substrate not so easily found. There are many other substrates that are excellent if used in making well draining mix.