Aside from the mold, the general color appears as though your E. obesa has had it. If it is soft, it is dead. Sorry for the bad news, but it can happen to the best of us and I can't begin to tell you how many of these I've lost that I've grown from my own seed.

It's definitely still alive as it is about as hard as a rock. I took a look at the roots recently and they were quite extensive and not rotting. Something tells me it won't stay living that long unless I get this mildew/mold/fungi situation under control.

I agree with the post above, and also yes, that tag is insane! If you decide to try again with a new plant, make sure it has tons of sun and water sparingly. I live in one of the driest parts of the U.S. and I water my cacti about once a month in winter (or less) and once every 2-3 weeks in summer. It depends on the species and of course on your soil and the humidity where you live. How often did you water this guy since you didn't follow the instructions (thank goodness)?

I watered about once a week, which in retrospect I believe was far too much. That damn label fooled me into thinking they were thirsty drinkers!

I'm thinking of getting this guy more sun and watering very little, which I'm hoping will kill off the mold/mildew. Maybe I'm just delusional, but I think he can still be saved. He doesn't have any rotting tissue or bad roots. If there's any other ideas to save this little dude, I'd love to hear them.

Is it living indoors or out? If indoors and you can put it out, gradually increase the amount of sun it gets over the course of a few weeks. If that is mold, perhaps the sunlight will kill it. Also, what kind of mix is it in? From the little spot I can see, it appears to be very peaty.

Nancy

Thank you all for the great suggestions! I'll be making a few changes and give an update when/if it responds well.