Can we have a "theory-mon"-ing thread? Basically, we suggest changes to items, abilities, and moves, plus add moves to level-up/egg/TM movepools. This entirely builds on pre-existing changes that've been applied, such as accuracy and power buffs to moves, or Prankster's new ineffectiveness on Dark-types.

Let me list some on my mind:
-Victini gets V-Create via level-up. Similarly, Relic Song, Dragon Ascent, and Secret Sword do not require a separate move tutor, as they too are level-up moves for their respective species.
-Magnezone's Sturdy is replaced with Levitate.
-Zygarde's Power Construct now converts a 50% or 10% Zygarde into 100% form as soon as it is sent in, with the 100% form having Aura Break. It also gets the move Recycle via level-up.
-Core Enforcer now runs off of whichever Zygarde's higher offensive stat is, and disables the ability of the target (or both opponents) regardless of whether Zygarde moved last or not.
-Zen Mode now triggers when Darmanitan goes below 75% HP, rather than 50%.
-Play Rough is now learned by Tapu Koko and Bulu.
-Guardian of Alola does not get the damage reduction while hitting through Protect/Detect, as unlike other Z-Moves, it cannot have the opportunity to KO an opponent in the process, since Guardian of Alola deals a fixed 75% damage of the target's current HP. This would not be OP because you sacrifice a Z-Move slot and it will never lead to a direct KO, whereas if you used something like a Hydro Vortex on a lv50 Golem with 20HP that used Protect, you'll probably still KO it whereas GoA would just bring it down to 5HP.
-Gale Wings stays active until Talonflame falls below 50% HP, assuring it can use Brave Bird more than once, but also essentially disabling the ability if it switches into Stealth Rock.
(continued in next post)