The canon PKMN World but with fan made regions and places as well!
Most fanmade regions there will be reachable through Dice and Marble Village (open ARPG!) which is a village on a secret island. It has portals to other regions you hardly get to travel to by ship or plane ;D
I also count each fan-region Ninchiru might create to this personal head-canon, as far as she allows my trainers to go there!
Fakemon
All fakemon of ARPG-PKMN-Trainers count towards my personal head-canon (Semi open to use: Your Trainer needs to legaly catch them in the ARPG)
All fakemon designed by Ninchiru count to my head-canon too, if I am allowed to use them (Do not use without permission)
All fakemon designed by myself, which are not part of ARPG-PKMN-Trainers do count towards my head-canon too of course xD would be strange if not (do not use without permission)
List: https://toyhou.se/PawstepFakemon/characters/folder:932444
Crossbreeds (Fakemon ARPG - Breeding for special Features)
PKMN with features of another PKMN. Example: A Pikachu with the fluff collar of an Eevee. Or a Morpeko with a Pikachu-tail.
Fusions / DNA-Evolution
Some PKMN can evolve into something else, when getting in touch with the dna of another PKMN.
Example: Mudkip evolves into Golpid. You get it when giving a Seaking-Orb to Mudkip or a Mudkip-Orb to Seaking.
What's the orb thing? These orbs are created by a PKMN that appeared in the Forest of the Fallen of Kasmar Region (a made up region). This PKMN takes other PKMN as hostage and steals energy from them with which it creates orbs. If it steals the energy of a mudkip, for example, it creates a mudkip-orb.
PKMN that can evolve with the mudkip-orb will react to it, when they get in touch with one. So they work similar to the normal evolution items.
Mega-Evolutions are permanent, if a certain item is given to the PKMN while doing the mega-evolution.
Gigantamax / Gigadynamax are permanent, if a certain item is given to the PKMN while dynamaxing. - They won't be gigantic all the time tho but can turn giga when ever they want or get told to.
Evil Guys
An organisation that experiments with PKMN to make each pkmn able to use each kind of move. And similar things. It´s actually similar to the Delta Species which I am a big fan of 8´D
Digimon
A group of kids once tried to bring Digimon into the "real" world (my pkmn head canon world) to make them replace PKMN there. Battles and stuff happened but in the end a secret team in the digital world took over the crazy ones and now they´re working with Silver (another mysterious character of mine) to bring Digimon into the "real" world without any evil plans or danger. So having Digimon in a PKMN Team is fine... I should re-think my problems with PKMN Fusions actually.
TemTem
Through portals Barkin created, trainers of my PKMN Universe are of course also able to visit the world of TemTem.
Animals
There are animals in this world. Nobody eats a Miltank where I come from. Not under my watch lol
Other Dimensions (also called "Realms")
Barkin discovered the existence of other dimensions (not talking about the ultra space). In some of them PKMN with special features can get found.