Dragon Frontiers was printed as part of a block of expansions set in the Holon region, a TCG-only region where scientists were heavily researching Mew and the powerful effects of crystals around the region, which seemed to change the types of Pokmon
The one downside is they are tight
You'll want to move as many characters to that location as possible , prioritizing characters with Reckless challengers, low Willpower questers like Simba, Scrappy Cub, and, if you can find her, Moana, Born Leader, who will ready all your other location-bound characters every time she quests
Generic fast mana like Ancient Tomb, Sol Ring, Mana Vault, and Grim Monolith alone represent so much value
You can't draw half a card, mill a quarter of a card, etc