I've had a pathos for the past couple years and it's been growing fine. I didn't water it well over the summer (I was away a lot)and I guess I overcompensated a bit in the fall and and watered too much. The plant is still lush and green but mold started growing on the soil. I worried a bit that it was mealybug but nothing was growing on the plant just the soil. It's a medium sized table plant and a little much for me to handle re-potting alone so I decided to remove the moldy layer and re-top with fresh soil. Everything SHOULD have been fine right? Except that I made the mistake of buying cheap potting soil, or should I say potting mud? I pretty new at houseplants and didn't realize until I watered it afterwards and the water wouldn't absorb for several minutes. The soil is VERY heavy and muddy. What do I do? I don't want to cause shock to the plant by fiddling with it too much. I also have a tight budget. Is there anyway to salvage this bag of soil (it is sterile, thank goodness) or do I need to be an expert to mix a proper well draining soil? Or should I just leave the plant alone and hope for the best? After all pathos are practically titanium. I'm not really worried it'll die but I do want to encourage healthy growth.

You are right. Pothos is a never-say-die plant! Or almost. But it does not like wet feet. You could add either Perlite or sand to your soil in the ratio 1(Perlite/sand): soil to improve its draining quality. I hope your plant continues to be lush!