You should take him and have him professionally groomed- either at a groomers or a vets office that does grooming. Fleas can nest under these mats and they just become infested with them and you'll never see them. The tail could be a condition called stud tail. It is caused by oil glands that are overactive. Once you get him groomed then the best be is to either keep getting him groomed or be sure to brush him good daily. You may even want him totally shaved down if he is an inside cat and depending on where you live.
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