I have a mean Maine coon who will not tolerate brushing. Every year he gets several large mats underneath on his belly and under his legs.
In the past, I have sedated him and had him shaved but the last time he came out of sedation, he wasn't the same for a long time. THE MOST IMPORTANT PART OF THIS METHOD IS TO USE A DROPPER AND PUT ONE DROP ON THE MAT AND ONE DROP ABOVE THE MAT.
The mats will loosen up in a couple of days and you can just gently pull them off or they'll fall off on their own.
Please do not use more than a couple of drops and please please do not cover your cats with olive oil or baby oil.. this is extremely dangerous as their livers cannot process these oils."