Were kind of a little bit of both, Tiffany says
However, its secondary effect is where the Information Gain lies: This attack does 30 more damage for each Energy attached to all of your opponents Pokmon. In a meta dominated by high-energy Ancient and Future decks, or the upcoming Mega Rayquaza ex which requires 4-5 Energy to swing, Mega Mewtwo Y ex can easily hit for 360+ damage for a three-energy investment
They often form the backbone of Limited decks, provide basic removal and combat tricks, and occasionally become format staples that punch way above their perceived power level
These cards are referred to as mass removal, board wipes, or board clears.
This Leyline isnt a must-have for token decks as it can be replaced with cards like King Darien XLVIII and Eldrazi Monument, and it even pumps your opponents' tokens, which is usually a no-go
I'd hesitate to call it a high-powered deck, as it's really not fully tuned with all the staples a deck like this would probably want