Beginner Gardening: What happened to my succulent when the other are all fine?, 3 by Emma519

Emma519 wrote:
My succulent has been slowly turning mushy from the bottom up. i think i over watered it but the other plants in the other ones seem to be doing just fine. Please tell me what i should do, i have never had succulents before these so I'm going off of a paper that was given to me when i bought the pot. I hope the picture i posted below help. Also the last one is a picture of when i first bought it. Sorry i dont know what types they are but if you know i would love to hear what they are. Thanks for your help.