Mana dorks, Viscera Seers, Azusas, Grand Abolishers, Scute Swarms, Laboratory Maniacs, Foundry Inspectors
I came up with the mechanic that met every one of Bill's requirements
Lunala 108 Alolan Meowth Dark 60 Scratch (20) Solgaleo 109 Alolan Persian Dark 100 Claw Slash (50) Fur Coat (Ability) This Pokmon takes -20 damage from attacks
Fortunately, most of them will become clear with a bit of experience, so if players jump into a game with good intentions, they're unlikely to run afoul of any community rules
The way abilities interact and reflect their lore is a testament to the design teams understanding of both universes
That said, one other great use of custom cards leans more into proxy cards: making versions of a card that never got released in your region or language