Legendary Pokémon.
These are not just powerful Pokémon. They are gods.
Catching them is not conventionally possible. Even a Master Ball, with a perfect catch rate, cannot keep them properly. They will destroy the Ball at the first available opportunity. The few who have caught one claim it had more to do with some test of virtue than battle.
As few have been caught, fewer have been studied in a lab, and none allow their bodies to be studied post mortem, rendering concrete information scarce.
When referring to a Legendary Pokémon in its role as a god, it is called a Divine.
When Legends die, they reincarnate soon after.
At times, Legendary Pokémon create Avatars. These Avatars are manifested fragments of the power and mind of the real deal, and allow them to explore and see the world without catastrophically damaging anything or disrupting the world around them. The Avatars can be beaten in a fight, but can fight on even terms with the great dragons like Dragonite, if they aren't even more powerful.
The Ultra Beasts will be listed in this volume due to their power, rarity, and obscurity.
A/N: Zocarik here.
Canon game stats and abilities are somewhat lame. Exhibit A: Groudon is the size of an elephant, weighs as much as a Cyldesdale horse, and can merely cause a drought for five turns outside of Primal Reversion. Compare that to the Anime which has Groudon be like a Kaiju, towering as a small mountain or at least a warehouse, and destroying everything just by sitting there.
Honestly, anime Mewtwo set the bar for me back in the nineties. Lowball his power: the storm was just powerful enough to devastate Kanto and destroying further regions would take more time. He maintained that, locked down all the moves from clones and their templates, and held his own against Mew which probably had decades or centuries experience on him. All without having any special affinity for any of those things the way others do. That cemented what a Legend is supposed to be.
Many legends have Pressure as their ability, and the hidden ability may be unavailable. Ho-Oh, Lugia, Birds, Beasts, Mewtwo, Deoxys, Creation Trio, and Kyurem all have it. From a gameplay perspective, it makes sense. If the player is not overleveled, that ability turns catching them into grueling endurance matches, desperately trying to survive the onslaught while weakening the target, and dealing with the rapid drain of PP. From a narrative view, it is lame. Even the Hidden Abilities can be sub-par for a virtual demigod.
Mewtwo has Unnerve (no eating berries). Really? Beasts have never been allowed their G5 and 6 abilities, and in G7 got Inner Focus. Not good enough and does not fit the theme of children of the phoenix. The Creation Trio, the firstborn children of Arceus, have Telepathy. Like the ability to dodge an ally's AoE moves like Surf during a double or triple battle is impressive in the claws of the creation gods.
Latios, Latias, and Origin Giratina all have Levitate. That's it? No shields or illusions or speed boost to evade with? No phantom attacks or anything like that?
In the games, wild Kyogre has zero ways to hurt Shedinja. Does that sound like a practical god of the primordial oceans, brought low by a shed bug skin? Did the Anime version look like something that could be meaningfully hurt by a shed skin?
Only the Avatars have canon game stats. The real versions are like the anime or PMD where you never quite KO them, instead just stunning them long enough to talk some sense into them. (really, see Rescue Team: when you beat the Birds in main story, they get up within a minute, ready for round two, and must be talked down.)
All cases in Anime where Legend vs norm Pokémon is not curb stomp involve mitigating factors in my mind. Latias and Latios were practically children with no real training. The Dream!Entei was merely a construct from hundreds/thousands of Unown. Virus!Groudon was destroying the whole region just by existing before it started using the tentacles to eat everything. Zoroark was about to die, and just would not let herself die until she rescued Zorua, even after getting attacked by Crown City Beasts, which only hit a few times anyway.