I'll just get straight to the leaks. Mostly stuff that Riddler has hinted but more in-depth. Please excuse me if I have mispelled something but english is not my native language.

About Ultra Beasts:

> UBs aren't catchable and have no typing, which means that everything is neutral against them. They become harder to fight as the story progresses, with the final battles being against them with 700+ base stats.
> UBs are from another dimension and try to replicate the first humans they encounter in order to replace them. The mission during the second part of the story is to destroy them before they become indistinguishable from humans.
> UBs are all based on invertebrates and body systems. UB1 is based on the nervous system, and Beauty and Expansion are based on the skeleton and the musculatory system respectively. There are also two other version exclusive UBs that are based on cephalopods and the circulatory and digestive system.

About New Pokemon:

> Type: Null has an unleashed forme with Protean. It's stats are pseudo-legendary tier and it was created by Aether Foundation.
> There is only one Type: Null and Gladion will eventually give it to you in order to fight the UBs. It's also vital in a Delta Episode-like arc involving the Sinnoh legendaries (Palkia, Dialga and Arceus).
> Morelull evolves into a fairy ring that has multiple Morelull growing around a bigger mushroom a la Dugtrio. Same typing and abilities.
> Comfey has a humanoid evo that uses its lei as a hoola-hoop. Same typing and abilities.
> Boundsweet has an evo based on paprika that is Grass/Fire. It's seeds are very sought out so the Pokemon is vicious in order to defend itself.
> Salandit's evo is of the same typing and abilities. It uses its throat as a way to store the objects it has stolen.
> Wimpod has a Gyarados-like evolution that looks like a giant shrimp with pincers near its head. Same typing.
> Jangmo-o is obviously a pseudo and its final evo is Dragon/Fighting.