This concept is based on "The Pokemon Emissary Among Worlds" by sweet_and_sour143. After death Arceus uses a soul from our Earth to be the person to spread pokemon throughout the multiverse and change their power systems to the pokemon system (fighting through the use of pokemon, ending disputes through pokemon, etc.).
The main character goes to different universes and judges them based on their technology level, overall moral code, and their opinions on the unknown. If their technology level is rudimentary enough to create pokeballs or has the resources to copy them if given an example it meets the first requirement. If the universe is over run with crime than it isn't an option, or if their are caste systems in place (slavery and similar things) than it also isn't an option. If it is neutral between bad and good then it meets the requirement or if has almost no crime than it meets the requirements. Lastly, what are their reactions on seeing supernatural phenomena. If they have a neutral or even positive reaction than it meets the requirements. If their first response is to try and kill it, capture for study, etc. then they do not meet the requirements.
The main character has the ability to telepathically talk with everyone on the planet no matter what, to spread the announcement of the introduction of pokemon. They can create pokemon and displace them back to the original pokemon world. They also have the ability to be intangible to any attack on their person, because they are an ambassador. They have the ability to telepathically contact anyone that has the ability to create pokeballs with their current knowledge.
When the requirements have been met then he can call upon Mew to spread pokemon throughout the world of choice. And he can call upon Xerneas to spread Apricorn trees for pokeballs and berry trees for the special pokemon berries. If they abuse pokemon after he has left, he can be notified and call upon Yvetal to enact a punishment.