Only the most major changes are listed here, a full list can be seen in the spreadsheet linked above.
Mechanics
Snow
Replaces Hail, works exactly as it does in Gen 9. Snow Warning and the move Hail now set Snow.
Freeze
Has received a complete overhaul, with the following changes:
- No longer immobilizing the afflicted Pokemon
- Affected Pokemon now lose 1/16 of their max HP at the end of every turn (1/8 in Snow)
- Affected Pokemon take 30% more damage from attacks (basically, every attack against them gets a Life Orb boost)
- Pokemon can still naturally thaw out of freeze, but the chance is now only 10% per turn
- Other methods of thawing out still work
- Fire-types are now immune to freeze
- The Snowball item has been added to the game and inflicts freeze when flung - this is the only guaranteed way to inflict freeze
- Facade is now boosted by freeze (and sleep) and Synchronize now activates if the Pokemon with it is frozen
These changes remove the uncompetitiveness of freeze while still making Ice-type moves scary for walls come in on, since the damage boost + chip damage might get them in range of an unexpected 2HKO.
Paralysis & Confusion
Paralysis and confusion now work like they do in Gen 9, except that paralysis still lowers Speed by 0.25x. This, along with limited Steel-type options and strong Dragons like Haxorus and Kyurem-Black, is why Outrage has been nerfed to 100 BP.
Moves
Defog
Now works like Gen 6 Defog, removing hazards from both sides of the field - While this is a crazy change to make on paper, it's actually quite low impact, since Defog options are extremely limited and the options that do exist (mainly Mandibuzz, Whimsicott, and Braviary) all kinda suck. Thus, hazards remain strong if you're not using an Excadrill to get rid of them, but you have a few new options for teams that absolutely need hazard control.
Teleport
Now switches the user out - DryPass: The Move, was originally supposed to a change to Baton Pass to unban it and add some more pivoting options, but I couldn't figure out how to stop Baton Pass from passing volatiles, so I put the changes on Teleport instead and gave it Baton Pass' distribution. This is why weird stuff like Liepard and Scolipede get the move.
Swallow & Spit Up
Both of these moves now have effects when you have no Stockpiles:
Swallow - Now heals 1/3 of the user's max HP when the user has no Stockpiles, 1/2 at 1, 2/3 at 2, and all HP at 3.
Spit Up - Now has 50 BP when the user has no Stockpiles.
This mainly serves to buff Swallow, now being a decent recovery option for Heatmor and Garbodor.
Items
Gems
Gems are unbanned, receiving a big power nerf, going from 50% to 30%, but in return they now also give the affected move an additional effect. Some notable ones include:
Dark - Removes the foe's item after dealing damage - Probably the best gem effect since its effect is uniquely permanent, turns 1 Dark move into Knock Off. I'd say that this is the second best gem overall and will probably be the most common one.
Electric,
Poison,
Ground,
Rock,
Steel - Lowers the foe's Evasion/Special Defense/Attack/Special Attack/Defense by 1 stage - These five gems all lower stats, with the best of these being Poison and Steel, as these normally awful offensive typings can be used to force switches or bust through walls with their defense drops.
Flying - Gives the foe the Telekinesis effect - This effect isn't terribly strong, but the Flying Gem will always have a use-case because of Acrobatics, though it's also kinda nice to guarantee hitting a second Hurricane after managing to hit the first one.
Psychic - Gives the foe the Heal Block effect - Longer Psychic Noise on any one Psychic move, can similarly force walls into awkward positions like Poison and Steel Gem.
Additionally, Unnerve now prevents Gems from activating
Light Ball
Now works on Emolga, which, along with a stat overhaul and minor movepool buffs, makes Emolga into a fun glass cannon.
Abilities
Speed-boosting Weather Abilities
With all 4 weathers present in the tier (more on that later), finding a way to unban the likes of Chlorophyll and Swift Swim felt like a good opportunity to further shake up the weather metagame, so they all been unbanned but with a couple changes:
- Chlorophyll, Sand Rush, and Swift Swim now only boost Speed by 1.5x in their respective weathers.
- Slush Rush now exists and also only boosts Speed by 1.5x.
- Drilbur and Excadrill no longer have Sand Rush
These give weather teams good forms of Speed control but said Speed control is only as strong as a Choice Scarf, often still requiring abusers to run Speed boosting natures, lest they get revenge killed by Scarfers naturally fast mons, being much more along the lines of Protosynthesis Speed-boosting in Gen 9. Plus, without Sand Rush Excadrill, the wielders of these strong abilities aren't particularly crazy, with the best for each weather being Seismitoad, Sawsbuck, Stoutland, and Beartic, who all have multiple other faults that keep them from being overwhelming, or even automatic inclusions on weather teams.
Snow Cloak / Sand Veil
These abilities take a page from VaporeMons and now make the Pokemon immune to indirect damage in their respective weathers, instead of increasing Evasion. They remain niche but really nice to have to avoid damage form hazards or Life Orb.
Sand Force
Excadrill also got its other weather ability nerfed, as Sand Force now only boosts the power of Ground, Steel, and Rock moves by 1.2x in Sand instead of 1.3x, making Excadrill and the unbanned Landorus much easier to handle in Sand.
Download
Genesect is unbanned, needing multiple nerfs to to do so, with one of them being Download. Now, the stat boost goes away at the end of the next turn, which makes it harder for Genesect to snowball after getting the right boost. This encourages its VoltTurning playstyle, but (spoiler alert) with Genesect getting a massive Attack nerf, said playstyle is much less powerful.
Future Gen Abilities/Moves
Along with the aforementioned Slush Rush, a couple future generation abilities and moves have been added as either unique buffs or flavor to a few mons

Samurott & Leavanny get Sharpness - Samurott also now gets Sacred Sword
Swanna gets Gale Wings (Gen 7+ version) - Swanna also got a big HP buff, making it a niche Keldeo answer
Bouffalant gets Fur Coat - Along with some stat rearrangement and movepool buffs, Bouff now serves as a decent blanket check to physical attackers
Eelektross, Emolga, and Stunfisk get Parabolic Charge, which is now a 65 BP Electric-type Draining Kiss clone - Mainly here to buff Eelektross as a bulky set up mon, since it also now gets Calm Mind
Cobalion gets Tachyon Cutter - Steel is still a bad offensive typing pre-Gen 6, but Tachyon Cutter's notable power jump compared to Flash Cannon makes it a great option on Coba
Terrakion gets Mighty Cleave, which is now 65 BP and no longer makes contact - Had to add this if I was adding Tachyon Cutter, you won't use it over Stone Edge but it exists. You'll find out what Virizion got in the next section, as it's definitely not Psyblade
Cinccino gets Tidy Up - Adds another niche hazard control option with some (literal) sweeping potential
Sawk & Throh get Upper Hand - Added solely for Reversal Sawk shenanigans, since Upper Hand makes it so that you can't get revenged by priority if you win the mindgame