A 100% raw meat diet can be done
The best thing to feed your cat is to give them 90% raw meat and, because raw meat doesn't have all the things cat needs, live it a half or handful of Royal Canin cat food. But if you sterilize the cat, you have to feed with food for sterilized cats only. If your cat's mouth smells bad, then feed it like this.
Dry food should never be fed with raw food. The slow digestion rate of dry food combined with the fast digestion rate of raw food means an upset tummy for the cat.
A special diet is not necessary for neutered or spayed cats.
A bad mouth smell usually indicates dental problems and needs to be treated by a vet.