There are several types of rare Pokémon, including Legendary, Mythical, and Ultra Beasts, throughout the history of the franchise. These creatures are unique even among other Pokémon due to their strength and rarity and are highly sought after by Pokémon Trainers as well as researchers. When someone really stops and thinks about it though, Legendary Pokémon don't make a lot of sense with the way they are portrayed throughout the Pokémon franchise.
Not only are there individual Legendaries found within every Generation of Pokémon, but each Generation also has a Legendary Trio where three Legendary Pokémon can work together to be even more powerful with the synchronization of their abilities. While these are very cool and fun to use in the tabletop card game as well as video games, it also defeats one of the major purposes of each of the Pokémon being Legendary. These are known to be among the rarest and most powerful, but they really aren't as rare as the term implies.
There Are Too Many Of Each Legendary Pokémon
Canonically, it is a bit difficult to say how many of each Legendary Pokémon there are. Originally, it was said that Legendaries were uniquely one-of-a-kind, but this was changed to later say that they are very rare. In video games such as Pokémon GO and Pokémon Scarlet & Violet, the Legendary creatures became some of the typical challenges for Raids, where players could then try to catch the Pokémon after defeating them and then move on to another raid to do it again, suggesting that there are many of these monsters around to be filling each of these Raids for trainers to collect. Once the inclusion of shiny variants is taken into consideration as well, the rarity of the normal Legendary Pokémon is a bit suspicious.
The Rules Surrounding "Legendary" Seems To Waver In Pokémon
Aside from the heavily implied idea that there is only one of each Legendary, there are some rules surrounding them which have changed over the years. At one point in the history of Pokémon, it was said that trainers could only catch one of each variety of Legendary. With the inclusion of Pokémon GO, and particularly with Shiny Legendaries making a debut, this rule disappeared and players can catch as many as they want of each kind. While Legendary Pokémon are supposedly the most incredible and powerful in the Pokédex, even some of these Legedaries can be woefully disappointing in their weaknesses and flaws.
Pokémon is not necessarily supposed to make sense, however, the titles of Legendary, Mythical, and more can all seem to blur together and even within the various games, the meanings change. Not all Legendary Pokémon are all that incredibly powerful, and there certainly is not only one of each, or even that they are very rare. Pokémon is a fun franchise, with fantastic video games, the TCG, anime, and more, but the lore behind some of it is a bit chaotic.