Hello I am a new leaker
Unfortunalely I have poor english
Here is a leak

The three new legendary have a special tera typing
When they terastalize with the good typing, they get a new form
The bird one is psychic but comes with flying
It becomes a big crystal eagle when it terastalize
The monkey is dark but comes with normal
Becomes a big crystal gorilla when terastalized
The dog is ground type but comes with grass
Becomes a big crystal bamboo wolf when terastalized
They will Introduce players to the new mechanic
Other pokemon can also have new forms

Region of the first DLC will have their own regional bird (normal/flying)/rodent (normal)

new regional forms and convergent pokemons

New snake pokemon line
First is a baby snake with little spikes (poison/ground)
Second is snake with big spikes (poison/steel)
Last is Hydra with spikes all over his back