yea i thibk its opuntia macrocentra. and yea lol its creepy spider

A mistake lots of folks make, even after drying in air for a few days, is to 'water-in' immediately after potting. Just adding dry soil to the pot can injure roots, so waiting another week or more before watering is good practice. Even if you do everything the right way, this can still happen. Fungal spores are everywhere. I lost a big Echeveria a couple of months ago to rot. It bloomed its head off for most of the summer and then just fell over. The stem had been half chewed through by a snail, allowing fungal entry. The plant had large stores of water and sugars in the leaves and stem, so a complete failure of the stem to transmit water from the roots was not noticed until too late.

I would start by getting it out of that cup. Get a pot with drainage holes(terra cotta preferably), cactus mix, and perlite or pumice. The new pot should be about one inch wider than the cup. A mix of 60% pumice or perlite with 40% cactus mix. When repotting get all the old mix off the roots. Don't water for a week after repotting. Now when it comes to the etiolated growth it would probably be best to cut those pieces off. Once you give more light the old skinny growth won't be able to support the new sturdier growth. Just take a clean knife and slice off the lanky growth. I would do this after you've repotted:). Do you live in a dry climate or humid?

I think it is a Mammillaria. The species I found that looked closest are: freudenbergeri, lloydii, roseoalba (but flowers light pink), uncinata, and winterae. M. uncinata had the most similar characteristics to you picture.