Unobtainable stuff for Gen VII, USUM

Items:

Items that are one-off:

1. Apricorn Balls

Unobtainable Berries:

1. Pokéblock Berries(besides Bluk and Pinap Berries, for Natural Gift)

Items that seem to be dummied out:

1. Elemental Gems 
2. Scarves
3. Relic Items
4. Flutes
5. Mulches

Others:

1. Odd Keystone 
2. Fluffy Tail
3. Shoal Salt
4. Shoal Shell

Pokémon:

Mythicals:

1. Alternate Color Magearna

 Unobtainable Hidden Abilities:

1. Heatran
2. Tapu Koko
3. Tapu Lele
4. Tapu Bulu
5. Tapu Fini

Edit(08.03.2018): Rowlet, Popplio and Litten-lines with HAs are now available with Pokémon Bank distribution.
Edit(17.11.2018): Zeraora has been available as event for a while now.
Edit(11.12.2018): Enigma, Micle, Custap, Jaboca and Rowap Berries will be made available through Global Link in Japan from January 8th 2019 through September 3rd 2019.
Edit(28.03.2019): Oranguru and Passimian are made available through Pokémon Bank distribution.