@needrain
Well it originally was firm and discolored but now it's a bit squishy. My one cactus that rotted had gotten discolored at the bottom and it was mostly firm but then a piece of the skin peeled off and there was black mold underneath. That was one of the ones that died. I'm scared of the same happening here. I do have four other cacti that do have the firm discoloring at the bottom but they're definitely not rotting as they haven't gotten mushy or anything. But this one has gotten slightly mushy which is of course concerning.
