Mega Meowstic has the same moves as the base form of Meowstic (which has different moves depending on its gender), but PokeAPI only assigns a single pokemon_id for Mega Meowstic. Since there's no good way to mark this, I've simply not included any moves for Mega Meowstic at all.

Do you mean that Mega Meowstic has a different learnset depending on if it's male or female? If so, we should make a pokemon resource for each of them and add the relevant move data to each. Otherwise, we should add the move data to the single Mega Meowstic.

Mega Meowstic has the same moves as the base form of Meowstic (which has different moves depending on its gender), but PokeAPI only assigns a single pokemon_id for Mega Meowstic. Since there's no good way to mark this, I've simply not included any moves for Mega Meowstic at all.

Do you mean that Mega Meowstic has a different learnset depending on if it's male or female? If so, we should make a pokemon resource for each of them and add the relevant move data to each. Otherwise, we should add the move data to the single Mega Meowstic.

Yes. Like all Mega-Evolved Pokémon, Mega Meowstic has the exact same learnset as its base form. But male and female Meowstic have different learnsets, so male and female Mega Meowstic also have different learnsets.

Splitting Mega Meowstic

I've updated pokemon.csv, pokemon_form_names.csv, and pokemon_forms.csv to split Mega Meowstic into separate entries for male and female. I've reused the existing ID for male Mega Meowstic, meaning that female Mega Meowstic is not adjacent (it ends up at the bottom of the list instead). I've also inserted the Mega Meowstic moves I had removed earlier.

In the documentation for Pokémon forms, is_default is described as "True for exactly one form used as the default for each Pokémon." However, it seems like every single Mega-Evolved Pokémon is set to is_default in addition to its base form, and many other multi-form Pokémon have multiple forms flagged as is_default. I've set this field to True for female Mega Meowstic to mirror what all of the other Mega Evolutions are doing, but to me it seems like it should be False for all of the Mega-Evolved Pokémon.

order seems to want forms of the same species grouped together, but is also a simple incrementing integer with no gaps. As a result, to insert a new form of Meowstic I've had to increment the order field for every Pokémon after Meowstic in the National Pokédex. (IMO, this would be better handled similarly to what Champions does internally, where they just allocate the last 3 digits to the form ID and the first 4 to the National Pokédex number, so that inserting a new form doesn't require incrementing all of the others; e.g. Mega Venusaur is 0006001. However, changing that structure would belong in a separate PR, so I've just stuck to what is already there.)

The documentation does actually note "Multiple forms may have equal order, in which case they should fall back on sorting by name", so theoretically it may actually not be necessary to insert a new distinct order value for female Mega Meowstic, but that doesn't appear to be what is actually done in practice.