It’s plausible some of these have been released for the Sword & Shield era and I’ve missed them (since my collection is non-active right now), but in my National Index checklist I included all Pokémon forms, and mentioned those which weren’t released as cards yet. So, here a list of those:
- Arbok Secondary Circular; Pokémon Ranger; Invulnerability; Attack; and Speed patterns (only the Main/Regenerative; Main Circular; and Dark pattern Arbok have been released as TCG cards)
- Crystal Onix (the actual crystal one from the anime, would have loved it if this got a card)
- Mega Pinsir
- Mega Gyarados (all the Mega Gyarados cards are shiny versions, the regular non-shiny Mega Gyarados is never released)
- Mega Steelix (all the Mega Steelix cards are shiny versions, the regular non-shiny Mega Steelix is never released)
- Mega Medicham
- Mega Banette
- Mega Metagross (all the Mega Metagross cards are shiny versions, the regular non-shiny Mega Metagross is never released)
- Mega Latias
- Mega Abomasnow
- Arceus Sky; Insect; Toxic; Stone; Spooky; Fist; Icicle; Draco; and Pixie Plates (only the No Plate; Meadow; Flame; Splash; Zap; Mind; Earth; Dread; and Iron Plate Arceus have been released)
- Deerling Autumn and Winter forms (only Spring and Summer form Deerling have been released)
- Sawsbuck Autumn and Winter forms (only Spring and Summer form Sawsbuck have been released)
- Genesect Shock; Burn; Chill; and Douse drives as well as the High-Speed Flight Configuration (only the No drive Genesect has been released as TCG cards)
- Vivillon Archipelago; Fancy; Garden; Jungle; Monsoon; Poké Ball; Polar; River; Sandstorm; Sun; and Tundra patterns (only the Continental; Elegant; High Plains; Icy Snow; Marine; Meadow; and Savanna pattern Vivillon have been released as TCG cards, and Modern and Ocean pattern Vivillon are present on the artwork of a trainer card)
- Flabébé Yellow; Orange; Blue; and White Flowers (only the Red Flower Flabébé is released as TCG card)
- Floettte Yellow; Orange; Blue; and White Flowers on separated cards (there is one Floette artwork containing all five colors at once)
- Florges Yellow; Orange; Blue; White; and Eternal Flowers (only the Red Flower Florges is released as TCG card)
- Furfrou Diamond; Pharaoh; La Reine; Dandy; and Debutante Trim (only Natural; Heart; Star; Kabuki; and Matron Trim Furfrou are released)
- Neutral Mode Xerneas (only Active Mode Xerneas cards have been released)
- Zygarde Cell (and the Zygarde Core is only available as Trainer card. Zygarde 10% Forme; 50% Forme; and Complte Forme are all available on cards, though)
- Silvally Flying; Bug; Poison; Rock; Ground; Dark; Ghost; Steel; Ice; Dragon; and Frairy Memories (only No Memory Silvaly cards are available, and the Grass; Fire; Water; Electrice; Psychic; and Fighting Memory are available as Trainer cards)
- Minior Orange; Yellow; Green; Blue; Indigo; and Violet Cores (only Meteor Form and Red Core Minior are available as TCG cards)
- Mimikyu Busted Form (only Disguised Form Mimikyu are available)
- Radiant Sun Phase Solgaleo (only the regular Solgaleo is available)
- Full Moon Phase Lunala (only the regular Lunala is available)
- Magearna Origin Color (only the regular Magearna is available)
And there are also a bunch of easy distinguishable gender differences which were never available on cards. Here my National Index checklist, if you want to check those. And here my current National Index collection to see all forms and gender differences that ARE available on cards (excluding gen 8 and Sword & Shield released cards).
Greetz,
Quuador