Plant Clinic - diagnosing sick plants 🌱

I would guess that you have root rot, I would get it out of that container ASAP to check the roots and let the soil dry out. White and/or stiff roots are good, soft and brown are bad. Rotting roots can kill the plant so you want to remove them. You want to use isopropanol to clean any scissors or tools used cut out bad roots to prevent spreading any of the stuff causing the rot any where else.

It looks like it may have travelled up to the middle leaf, if the leaf doesn't dry out and continues to spread toward the stem, cut off the yellowing/brown part or even the whole leaf with clean scissors.

The darker nubs on the stem are actually roots, so you can propagate from those if you need to. Just cut the stem an inch or so below some of them, let the cut dry a little bit (5-10 minutes), and put it in clean water for a few weeks. Make sure to change the water occasionally.

Pothos are pretty hardy plants, so you don't really need to rush while working through the roots. I would not put it back in that soil if you find you have a lot of rotting roots. It would be fine for a healthy plant, but yours needs some love (e.g. ignore it once you've dealt with the bad parts). If you don't have any potting soil, you'll have plenty of time to get some if you've already started.