MEGA Update!

Added all of the Pokémon with regional forms! This also includes their evolutions if they have one.
Additionally added the lines of the Pokémon introduced in Pokémon Legends Arceus.
Some of the evolutionary methods of these Pokémon were altered to make getting their evolved forms easier if they are Partner Pokémon.

Spoiler

An ordinary Stantler now evolves into Wyrdeer after using Psyshield Bash 30 times, while Partner Stantler uses the original evolution method in just knowing the move.
An ordinary Hisuian Qwilfish now evolves into Overqwil after using Barb Barrage 30 times, while Partner Hisuian Qwilfish uses the original evolution method in just knowing the move.
Regional forms of Pokémon that evolve in a completely different way that their original variants now use the same evolutionary method that their original variants use if they are Partner Pokémon (ex. Partner Alolan Sandshrew now evolves into Partner Alolan Sandslash by level-up instead of using an Ice Stone, sparing you the trouble of having to search for one). Be forewarned, though, this only applies to some of them, not all of them.

Ability errors in Partner Pokémon have been fully corrected, so now every Partner Pokémon has the correct Abilities. This excludes purposely changed Abilities.
Changed the Partner Mudkip line's Hidden Ability from Damp to the much more useful Sand Force, allowing the line to be very effective in sandstorm teams in addition to already being amazing rain sweepers.
Added the Tinkatink line! Replacing Pickpocket, now you can cause havoc with the Partner line's new Hidden Ability: Huge Power! (Tinkaton gets Guts instead because it's funny)
Every Partner Pokémon available so far, including the newly introduced ones, have received behavioral updates. They now have their behaviors from the mods they originate from, but those who haven't yet received original behaviors received some changes to declutter them.
Some Legendary and Mythical Pokémon have gotten additional requirements to get their Partner flag.

More Spoilers

Lugia now requires the Legendary Birds (Articuno, Zapdos, and Moltres), specifically the Kantonian variants.
Ho-Oh now requires the Legendary Beasts (Raikou, Entei, and Suicune).
Rayquaza now requires Groudon and Kyogre.
The Pokémon of Myth (Dialga, Palkia, and Giratina) now require the Lake Guardians (Azelf, Uxie, and Mesprit).
Arceus now requires the Pokémon of Myth.
Regigigas now requires all five of the Legendary Titans (the Regis).
Keldeo now requires the other members of the Swords of Justice (Cobalion, Terrakion, and Virizion).
Landorus now requires the other Forces of Nature (Tornadus, Thundurus, and Enamorus).
Zygarde now requires Xerneas and Yveltal.
Pecharunt now requires the Loyal Three (Okidogi, Munkidori, Fezandipiti).
Keep in mind that the original requirements are still present and have not changed, and also keep in mind that the required Pokémon must have the Partner flag themselves for it to count.

EVEN MORE SPOILERS!

Added in a special variant of Partner Wooper, obtainable by maxing out the EVs in both HP and Attack and giving it the nickname "Woop_Woop" (yes, that's how it's supposed to be spelled). Anyone who has seen SmallAnt1's video titled "How to crush Pokémon Platinum with a single Woopy Boi" should recognize this little boi.

Partner Pokémon