Although there is a large number of Legendary Pokémon that can be captured in the games, many of them should never be caught. Being caught could lead to some disastrous consequences, and in the worst-case scenarios, these consequences could lead to the destruction of the world.
The Legendary Pokémon usually affect the balance of nature and serve as protectors of Pokémon in the wild. Some are so crucial that different parts of the world require them to thrive. Other Pokémon would not be able to stand being trapped in a ball and forced to battle, especially if they are the type of Pokémon that do not like to fight unless they absolutely need to.
10 Mewtwo Wants To Be Free
After countless years of unethical experiments, Mewtwo was created in an attempt to design the world's strongest Pokémon. After discovering that it was a clone of Mew, Mewtwo grew angry, wondering what his purpose was as well as what his place in the world meant.
After being convinced by Giovanni to become his puppet and tool of destruction, Mewtwo grew resentful of humans, escaping and creating a clone army. Although he decided against attacking humans after meeting Ash Ketchum, he just wants to live in peace with the other clones.
9 The Legendary Bird Trio Control The Weather
When one of the legendary birds is captured, the climate of the world is drastically changed. Suddenly, storms appear out of nowhere, as well as quick bursts of rain and snow even though they are out of season.
This leads to Zapdos claiming Moltres' territory, and getting captured makes the legendary birds so furious that they start attacking anyone and everyone that they see, including each other. A fight between them is cataclysmic and can be world-ending.
8 Suicune Purifies Lakes
Suicune has the ability to purify any body of water, but it most notably purifies the Lake Of Life. The Lake Of Life is a lake located in the Johto region which is capable of miraculously healing Pokémon. Suicune's existence in the wild is essential for the well-being of the environment it exists in.
Suicune is also a very elusive Pokémon, always on the move as it likes to run from place to place. A Pokémon like that wouldn't be able to stand being in a Poké ball.
7 Rayquaza Guards Against Extraterrestrial Threats
It is essential for Rayquaza to stay up in the skies in order for it to protect the planet from danger that approaches the planet from outer space.
In the original Pokémon Mystery Dungeon games, a giant meteor is falling towards the planet, and Rayquaza is the only Pokémon capable of destroying the world-ending threat. Rayquaza was the world's only hope in ORAS, as it was able to fly high enough to intercept Deoxys.
6 Calyrex Spreads Bountiful Vegetation To Harvest
Calyrex played an important part in the Crown Tundra. It was known as the King of Bountiful Harvests because it was able to bring plentiful harvests to the icy land every year. It has saved both people and Pokémon on multiple occasions.
It can heal wounds, mend hearts, and even move entire forests. As a king, it behaves like one, and it doesn't seem fitting for a Pokémon so willing to help others to be bound to one trainer.
5 Arceus Is The God Of Pokémon
Arceus is so powerful that it not only created other legendary Pokémon, but it even created the entire universe. It can recreate the legendary creation trio in the event that one of them is caught, and it has power over time and matter.
Arceus protects the world from cataclysmic events when necessary. Arceus has the kind of power that no trainer should be able to wield, as even a tiny irresponsible decision would be dangerous.
4 Shaymin Transforms Wastelands Into Lush Paradises
Shaymin is another Pokémon that is good for the environment. It is capable of ridding the air of deadly toxins by dissolving them. The polluted air taken into its body is converted into water and light, which it then releases back into the air.
Shaymin can also transform even a ruined land into a lush field of flowers. Not many Pokémon have power that can heal the land like this, and being trapped in a Poké ball would keep it from doing more good deeds like this.
3 Kyogre Creates Floods
Kyogre is one Pokémon that should be left alone, as it has the power to flood the world if it is awake by summoning enough rain to expand the seas. Kyogre flies into a blind rage the moment it sees its long-time enemy, Groudon.
However, Kyogre can be a peaceful Pokémon, capable of doing good. It has been known for bringing rains to areas that were suffering from drought, saving many lives in the process.
2 Necrozma Rampages In Search Of Light
Necrozma would be a dangerous Pokémon to have. It only acquires energy by absorbing light, and is willing to go on a rampage in order to obtain it. Without enough light, Necrozma stops moving completely.
In order to survive, it collects light and fires off laser beams at anyone who tries to stop it. When it does gather enough light, it becomes Ultra Necrozma. In this form, its body becomes 10,000 degrees Fahrenheit, melting everything around it.
1 Lugia's Wings Are Too Powerful
Lugia spends most of its time below the sea, and for good reason. Its powers are so strong that resurfacing can cause a lot of unintentional destruction.
A flap of its wings can set off a storm that can last for a total of 40 days, and its wings are able to tear apart houses and cliffs with no effort at all. It also serves as a guardian that intervenes when the legendary bird trio members begin to fight amongst themselves.