The only thing stopping this seeing more play will be the quantity of decks that actually want to play it
Shadowless (21 cards, including two rare, seven uncommon, and twelve common): #18 Dragonair, 23, 25, 26, 29, 46 Charmander, 48, 50, 51, 55, 56, 59, 60, 66, 78, 80, 84, 94, 96-98
When building a list of the most expensive, you have to refine your discussion to either include or exclude these three sets, as you would never make it to a consideration of the expansions or later traded cards without excluding these
Sundial of the Infinite: While not a spell itself, this artifact lets you end your turn by using its ability
CGC highlighted how they worked closely with Takumi Akabane, one of the original designers of the card game, to verify the cards' authenticity