Origins and Universal powers || Active legends || Exceptions

TL;DR

Originally, humans did not exist in the world, and so legends existed as just pokemon - most of which had an animal level of intelligence. Everything was fine and cool until humans were introduced by the Sky Mother, and said humans became advanced enough to team up with pokemon and build societies.

Humans were engaging with legends in a mostly negative way, and some legends had even been killed. To create balance, Arceus created a 'law' that made legends both human and pokemon, and the law was slowly set forth in the world.

Existing, living legends were granted with human-level intelligence, as well as the ability to shift into a human form, while the legends who had been killed had their powers and role appointed to an emissary - a revived human who had a connection to the legend, somehow.

In the way it currently works:

• Legends can shift between human and pokemon forms, as well as a god form that is a bit of a mix of the two. 
• Legends only die if both their pokemon and human forms are taken out, or die immediately of their god form is defeated.
• If a legend is killed, a new emissary is chosen randomly from a dead human with a connection to the legend somehow. This can literally be as arbitrary as 'they went to a church for them like once'. It Just Works!
  • Dialga and Palkia don't follow this rule, and instead, a random child will be given the role from birth and awaken their power sometime later. This is an even WORSE decision but Arceus trusts a New Person with the roles of Dialga and Palkia more and an Old Dead Person.
• All legends human forms stop physically aging at age 21 and cannot die from old age. If the revived emissary died before then, they'll continue to age up until that point.
  • Legends are able to freely modify their human form, so they can appear older if they so choose.
• Legend's dual identities are largely unknown and kept secret from the majority of the population, who only really knows them as pokemon. The only people who really know are either friends of the legend themselves or certain religious groups. It's kept a secret because those who let others know get their ass kicked REAL FAST.
• Only one of a certain legend can exist at a time, with some exceptions.
• Mythical pokemon are also considered legends, save for any that fall under exceptions.