All right, I've done some testing of my own, and here's what I've found:
When you Dynamax Silvally, Multi-Attack will take on the Max Move of the type of Memory Silvally is holding, if any. It will come up in move selection as Max Strike, and it'll say "Effective" or "Not very effective" based on the Normal-type, but it will come out as the Max Move when Silvally executes it. For instance, if you're up against a Steel-type and Silvally has a Fire Memory, you will see "Max Strike - Not very effective," but if you select it anyway, it will become Max Flare and deal super-effective damage. However, Multi-Attack is at 120 base power, and when it becomes a Max Move, it drops to 95, so you might be better off keeping Silvally as is, especially in Max Raid Battles if other people are present. The one type where this might be advantageous is Fighting, since Max Knuckle's power is lower than the other types and 95 plus the Attack boost might be worth it.
Dynamaxed Weather Ball has a power of 130 and, if it's raining, sunny, hailing, or sandstorming, will change itself to Max Geyser, Max Flare, Max Hailstorm, or Max Rockfall respectively. They also remain at a power of 130. Like with Multi-Attack, it will be displayed as Max Strike, but, if memory serves me right, will accurately reflect whether something is super-effective, effective, or not very effective. Max Geyser and Max Flare, of course, receive the damage boost from the weather conditions. However, since said weather has to be present to turn into these moves, they are not capable of setting the weather themselves. Weather Ball on a Gigantamax Pokémon that matches up with its G-Max move becomes that G-Max move (G-Max Wildfire on Gigantamax Charizard if it's sunny, G-Max Resonance on Gigantamax Lapras if it's hailing), even if it displays as Max Strike. Nevertheless, you could use Weather Ball on a Dynamaxed or Gigantamaxed Pokémon to keep your opponents guessing how your Jolteon suddenly used Max Flare or how Torkoal suddenly threw out Max Geyser (as situational as it is).
The Pokérus can now spread by running from a battle. It can also be spread by participating in a Max Raid Battle. To my knowledge, it cannot spread from one team member to another in a Max Raid Battle, but I have only battled with strangers using a Pokémon in an infectious stage of the Pokérus.
Ice Face, as documented here on this site, can only be restored from Noice in two ways: if Hail is set up that turn or if Eiscue is switched in while hailing. Bulbapedia says Ice Face is restored only once per setting of Hail, but this is incorrect, as Eiscue can regain Ice Face multiple times if it switches out and back in. Bringing in a Pokémon with Snow Warning or using Max Hailstorm counts as setting Hail, and Eiscue can restore itself. Now, what I find
real interesting is that if you attach Rocky Helmet onto Eiscue and damage from a physical contact move causes it to go into Noice Face, Eiscue will not take damage (unless the user has an Ability nullifier like Mold Breaker or Stalwart), but the user of the attack will still lose 1/6 of its maximum HP from Rocky Helmet anyway.
No but I wouldn’t be surprised if one day they decide to have introduce a region which happens to be Yungoos’s original habitat
Mongooses are native to the Indian Subcontinent (they are present in India, Pakistan, Bangladesh, Afghanistan, and Myanmar). Yungoos and Gumshoos, I would say, are probably native to the same as-of-yet unknown region as Cufant and Copperajah. It would be interesting to get a region based on this part of the world. Maybe we'll finally get a proper peafowl Pokémon.
For the record, Corphish and Crawdaunt are based specfically on
Procambarus clarkii, best known as the Louisiana Crawfish or the Mudbug. Its natural habitat is around the Gulf of Mexico, but it is a notorious invasive species in many other parts of the world. They are present in Japan, UK, and France, but they remain limited in numbers and have stabilized themselves within the native ecosystem, which might tie into why you only see Corphish and Crawdaunt in certain spots in these games. (On the other hand, they're running wild in southern Europe, Kenya, and parts of Southeast Asia.) If they ever make a region based on the southern or southeastern United States or northeastern Mexico, they'll likely identify that region as where these Pokémon originated.