- There are 104 new Pokemon. Galar forms are in, like the other leak implied with Meowth. "Sirfetch'd" is actually a Galar form and does not use that name, but the leaker may have called it that to paint a picture of its design. Its leek gets treated more like a cane as well as a color swap to black and white.

- This time, representation is scattered among all past region Pokemon unlike with Alolan Pokemon just being Kanto. Some examples will be the Gulpin line (they'll look more like sweets) and the Dwebble line (They'll be much more grassy and green).

- The majority of Kanto Pokemon will return. Strong representation from each other regions as well (though less than Kanto), totaling to a regional dex size of over 600+ Pokemon to make up for not every Pokemon being in the game. Many will only be acquirable through events and Max Raid Battles that get rotated around.

Dynamax levels only increase total Pokemon health and go up to level 10. At level 10, some Pokemon gain new "Gigantamax" forms.

- Skwovet is the standard rodent you will find mostly in early routes.

- Lofinch is the standard bird you will find in early routes as well, based on the Goldfinch with a love theme.

- Wooloo evolves into Puffluff. It's wool gets even larger, but it looks more adult like in its features.

- Raboot's evolution is called Athlabbi.t and will be Fire/Fighting, based on an athlete.

- Grookey evolves into Drumunkey. Drumunkey evolves into Bongorilla and will beat a drum to fight. Bongorilla is a Grass/Rock type.

- Sizzile and Intelleon leaks are correct. Intelleon is Water/Ghost.

- Zamazenta is pure Steel. Zacian is pure Fighting. Eternatus is pure Dark. You will encounter these legends and the story behind them after the seventh gym.

- Team Yell's grunts don't know much about their leaders. They go around causing ruckuses and trying to interfere with Pokemon battles and larger events. They're frequently mentioned as troublemakers on television and by locals in various cities and towns. Their main ive seems to be a lot more simple and harmless compared to previous teams, but the leaders are actually using their grunts to distract away from their operations. They are researching how to control Eternatus, in order to defeat Zacian and Zamazenta, the two guardians of the Galar region, in order to take it over.

The gym types and order is Grass (Milo), Water (Nessa), Ground (Kabu), Fairy (Opal), Fighting (Bea), Dark (Jora), Steel (Daron), and Normal (Lina). The Normal gym is directly in front of the Elite 4 and isn't a public stadium like the other seven. The Elite 4 reception is the first thing you see when you walk in, with her gym being accessible by entering a different room. Once you beat it, Leon will congratulate you and let you know he's waiting on top of the tower.

- The Elite 4 system has changed to be more like the Battle Frontier. After clearing the normal gym, your Badge Ring is completed and you're able to challenge the Elite 4 by speaking to a receptionist at the previous room before you challenged Lina. Each member is in a different building with a unique kind of challenge. You can challenge the first three in any order. 

- Enya (Ghost) is in the clock tower building to the left. Lyric (Flying) will be in the Ferris Wheel building and has a Chatot that can Gigantamax. Colt (Bug) is in the red building to the right. 

- Then, you go back into the building that holds Lina's gym. There is a guard standing in front of a different door that leads to the tower. He grants you access to the base of the tower, where the fourth Elite 4 member, Claude (Psychic) awaits. Upon beating him, there is an elevator that takes you to the top of the tower where you battle Leon. His Charizard has a Gigantamax form.

- Becoming champion unlocks some of the city surrounding the Elite 4. The area you can explore is not as big as it looks on the map, obviously. It is post-game content with several battle facilities that refresh daily, and markets that sell various hold items, TMs, and more items previously inaccessible. More Pokemon will start spawning in the Wild Area than initially.

- There is a Battle Tower system in the industrial city at the center of the map. This is also the city for the seventh gym, Steel. However, it is locked for a while before you can challenge it.

- The Wild Area looks a lot better than in the play test build. They had to crunch the most stable version for E3. The notorious tree has better textures.

I can't say anything more. Posting this many details is already risky.