These are two tweets from the leaker Khu.
The first could indicate the number of new Pokémon and the second the number of forms for each part of the DLC.
7 Pokémon in Part 1 (+ 6 Forms)
- Dipplin
- RFake (+ 1 Form)
- RFake evolution (+ 1 Form)
- (New Form for old Pokémon)
- Okidogi
- Munkidori
- Fezandipiti
- Ogerpon (+ 3 Masks/tera forms?)
8 Pokémon in Part 2 (+1 Form)
- Archaludon
- Dipplin Evolution?
- ???
- Raging Bolt
- Paradox Entei
- Iron Crown
- Iron Terrakion
- Terapagos (+ Tera form)
1 Pokémon, probably Mythical via special distribution (doesn’t have another form)
Both RFake and Dipplin evolution could be another unique Pokémon
Source and images from: Centro Leaks / ElChicoEevee / Kaphotics on Twitter