Old thread died so here is a new version:

Assuming that there are going to be 500 Pokemon in the Galar Dex, with 100 new ones, fill in the other 400 that you want in the dex. All forms count as 1 mon.
Hard Mode: you must include every pokemon that was already announced to be in the dex (Check Serebii)
Realistic Mode: you must also include every KANTOOO mon & associated evolutions/babies in the dex as well.