Could be thrips or fungal gnat larve.

Mammillaria herrerae v. albiflora?

Oh lol in the time it took me to type the reply Aiko replied with nearly the same information

The side growth is just an offset nothing abnormal there. The top growth is a spot where the plat has gotten inadequate lighting and grown thin to try to find more light, the "bulbous growt" is where the plant had reverted to a more normal growth. Unfortunately the skinny part will never f...

50% pearlite and 50% coir it drains pretty freely and doesn't stay wet for more than a couple days

Very nice post James! I have had bad luck with melocacti, but I think one was over watered and the other one may have been under watered oh well. Im going to keep trying because the plants are just so darn cool! Thanks for the post that was s very cool save! I especially like the aberrant one with t...

Always a shame to lose a plant. You could try to graft the individual tubercles.

Obregonia dengrii

Sorry I tried to post a photo but it won't go. I will try again and we will see if it will link.

Many can be grown outside especially if you put in a raised bed and a winter water covering. I have many echinopsis and trichocereus hybrids as well as cylindropuntia, opuntia, and echibocereus. So far they all do fine.

Sure. Germination wasn't great (I think I only sowed 10 seeds though) but I will have to wait for better light in the daytime.

From my experience with them they are relatively fast.

I kept in a bag for 8 and a half months and they look great right now. I have since removed them and they are doing pretty well.

Yes if you act fast. Cut below the infection with a sterile knife if you don't see bright green healthy tissue yet keep cutting until there is. The stock (probably hylocereus) will likely survive.