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Tried to do a quick summary of the setting using a combination of Bulbapedia, that card lore video, and the JP TCG article.
EX Legend Maker (JP: Mirage Forest)
>location: Mirage Forest
>Mew is prominently advertised, but not mentioned in Holon lore
>inside the Mirage Forest is a Power Spot that would give people a surge of energy through their bodies and be healed
>researchers established a village named Holon at this Power Spot to unravel its mysteries
EX Delta Species (JP: Holon Research Tower)
>location: Holon village
>almost all Pokémon cards feature a landmark or an environment that matches with the village's overview image
>the symbol for Metal type is prominent, including the research tower's layout
>the magnetic field from the research tower caused the Pokémon living around Holon to change into types abnormal to them
>said change is dubbed Delta Species for being the fourth discovered Pokémon variant after Normal, Extra, and Star
>Holon's Pokémon were also discovered at this time; Pokémon that can change the energy within themselves and can also become energy
EX Holon Phantoms (JP: Holon Phantom)
>location: outside Holon village
>landmarks feature more ruins, a lake with a monument, and a mountain range surrounding parts of the lake
>the lake monument resembles the symbol for the Metal type
EX Crystal Guardians (JP: Miracle Crystal)
>location: a remote island far from Holon village
>the island has little human activity and is filled with naturally growing crystals said to grant special powers
>said crystals in this expansion have an effect that negates or neutralizes
EX Dragon Frontiers (JP: Offense and Defense of the Furthest Ends)
>location: an island chain beyond the horizon
>inhabited by natural Delta Species
>a floating island surrounded by clouds is seen in the JP packaging artwork and several Pokémon cards
>Holon Legacy (JP: Holon's Holy Site) features a megalith that also resembles the symbol for Metal type