I have found this article about the cost for trades. It states that:
Standard Pokémon Trades:
Regional exclusives
Forms you don't have in your Pokédex (think Unown, Alolan and Castform)
Any other Pokémon not in your Pokédex that isn't Legendary or Shiny
Special Trades:
Legendary Pokémon
Shiny Pokémon
And for the trade costs (depending on the friend level
Standard Pokémon 100 80 8 4
Shiny or Legendary (Owned) 20,000 16,000 1,600 800
Shiny or Legendary (Unowned) 1,000,000 800,000 80,000 40,000
Here is my situation:
I only have the Armoured Mewtwo, not the regular one. If I trade with someone for a normal Mewtwo, is it an owned legendary trade or an unwoned legendary trade?
I only know, that regular Pokemons that are shiny or with skin (Pikachu with hats) count as an owned Special Trade, if you only have the regular one.
Best Answer
According to this reddit thread, the following will occur while trading
Each Pokémon that have variants, such as costumed, forms, or alolans, has a base and non-base forms. Base is considered the original version, such as normal Mewtwo. Non-Base would be any variants, such as Armored Mewtwo. If you have the base form, but not the variant, the variant will be considered unowned. If you have the variant, but not the base, then the base will be considered owned.
To test this, I used two accounts - Account A had both forms of Exeggutor and Account B only had alolan Exeggutor.1 In the confirmation screen for accepting the trade for regular Exeggutor and alolan Exeggutor, the trade was considered an owned and did not count as a special trade despite Account B not owning a regular Exeggutor
1 No Pokémon were harmed during this experiment