alright so i feel like a newbie not knowing this but...
with pokes that change form (giratina, rotom), do you have to have
multiple of those pokemon to satisfy the form change critera? like,
a rotom for each form change, and two giratina (origin and non
origin)? does this also apply for mega evolutions?
The way in which PH's pokedex works is that you lose the dex
entries of pokemon you don't currently own even if you previously
did. This applies to normal evolution, mega evolution, and form
changes (so when your pokemon evolves, you lose the first
evolution's dex entry if you don't have another one).
Therefore, if you want to own and have the dex entries of all the
different forms of rotom (for example), you do need to have 9
rotoms.