Not only are you limited to one copy of a specific Radiant Pokmon (e.g., one Radiant Greninja), but you can only include one Radiant Pokmon of any kind in your entire deck
Pokemon itself only officially labels cards Common , Uncommon , Rare and Promo on the card face
Technically you can farm cards for free if you are good enough
I would cast Cunning Wish and grab Mudhole and play it as an instant to slow that engine down
The Infinity Stones An indestructible mana rock that enters untapped and has an activated ability that makes it as relevant on turn 8 as turn 2 is a recipe for a busted card, and thats the template Wizards has given the Infinity Stones
Command Beacon can help you put Lumra back in your hand and avoid the Commander Tax, while Mirrorpool can copy key pieces or help create additional Lumra-style value without paying full price every time