En el Japó, Holon Research Tower va ser llançat després de Mirage Forest; however, due to a translation issue, the sets' releases were switched in English-language territories, causing the set to be released in North America and the United Kingdom just three days after its release in Japan.
However, due to Pokémon Organized Play's prereleases, for the first time in the history of the TCG, the entire set was available in English before in Japanese.
L'expansió presenta el Holon Research Tower, situat al centre del Mirage Forest (que es va introduir en EX Legend Maker, per tant, havia de ser llançat abans d'Especies Delta); és la llar dels científics que fan recerca sobre Mew i altres nous i estranys Pokémon. These Pokémon have been altered by a wave of electromagnetic radiation produced by an experiment gone awry at Holon labs. The result is a new species of Pokémon called the Delta Species, symbolized by the lower-case delta (δ). These new Pokémon possess types different from their original and some, in their fully evolved forms, are partially tipus Metals. They could be considered a counterpart to Dark Pokémon in the EX series. EX Delta Species also introduces Holon's Pokémon, which are unique as they can double as Special Energy cards, and new Trainer cards which centralize themselves around the Holon Tower community.
This set contains only 3 Pokémon-ex, a record low for any set in the EX series.
The holographic rare design changed exclusively for δ Delta Species Pokémon, with the card border and Pokémon itself featuring a plain holographic treatment.
The reverse-holographic design for this set is similar to that of the new holographic rare treatment, with same foil used but only on the background image. In addition to the background, name text and rarity symbol, the reverse-holographic versions of the holographic rares now have a holographic border and HP text. All reverse-holographics feature the EX Delta Species set logo.
The secret box topper card for this set is Azumarill.