*I still can't post picture although I've tried the camera icon before I even typed anything, but no luck.. I'll post the photos in comments.
I'm trying to figure out what it wants. This spiky plant doesn't seem to like being wet. The photos are from before I change the potting mix. The mix was dry when I bought it. While still in its original pot, I watered it once, perhaps a week after I bought it by submerging the pot (my go-to method to ensure roots get water). Just a day after, it started to turn to mush, so I unpotted it, removed all the soggy soil and separated all mushy parts, then left it to dry. I've since repotted it in my usual mix for succulents (orchid bark, small rock chips, and a little bit of potting mix for flowers which looks like damp, smaller-sized orchid bark). No water yet, it's been almost two weeks and seems fine. No further mushiness.