Not all Pokémon are free to catch in the wild. Sometimes, it is an effort to prevent extinction. Sometimes, it is the magnitude of the threat some Pokémon present. For these reasons and more, catching a Pokémon described in this book is prohibited without the proper licensing.
Class D Restricted Pokémon are simply sources of some medicines or raw materials that are controlled. Anything on this list can be farmed for a sellable product. Examples include Miltank and Parasect for MooMoo Milk and medical spores, respectively.
Class C Restricted Pokémon are rare. Everything on this list is endangered. Catching one requires registering for the Endangered Pokémon Repopulation Program.
Class B Restricted Pokémon are dangerous. They may not be aggressive, but they often do not understand how soft and squishy humans are compared to them. Catching them requires a Class B License. Some are not dangerous, but produce byproducts that qualify as dangerous drugs.
Class A Restricted Pokémon are the most dangerous, difficult to train, and prone to destruction of all Pokémon. Most make their respective region's lists of 'Known Human Killers'. Each species on this list has an independent license to catch it. No member of the evolutionary line may be caught without registering. Having a whole team of powerful fighters to keep a fresh capture in line is necessary. Failure to control one has a jail sentence attached. Lacking the appropriate license has an even steeper jail sentence. All of these Pokémon are aggressive, temperamental, or capable of mass devastation when angered. A skilled trainer can bring out their gentler sides.
Hazard Class Pokémon are not like other restricted Pokémon. They are dangerous in the same way as a storm or volcano is. They do not act to hurt others, they just exist. Any Pokémon with the Hazard Classification is a constant threat to everything around it because they influence their environment into a state of extreme danger. The registration is for the safety of everyone near the Pokémon.
A/N: some of these will be friendly mons that should be restricted for industrial or health reasons. Others will be restricted for violence.