What is the Delta Species in terms of TCG?

Question

like I had an electric totodile and psychic treeko. it says they're a delta specie on the card

i just want to know everything about that set

Answer 1

δ Delta Species (Japanese: δ-デルタ種 δ-Delta Species) are a special kind of Pokémon found in the TCG. The term is often shortened to δ, DS, or Delta. They first appeared in the EX Delta Species expansion, and were last released in the EX Dragon Frontiers expansion.

Pokémon apparently became Delta Pokémon if they were exposed to electromagnetic waves that were caused by scientists trying to find Mew.

As such, these Pokemon "change" into another Type, but they still keep their weaknesses that they usually have.
Now, Dual Type Pokémon will have a Secondary typing of Metal.

This Delta status still lets Delta Pokémon evolve into Non-Delta and vice versa.

In terms of card design, δ Delta Species have a coil design going around their image border, and the evobox circle becomes a large letter δ; Basic Pokémon have an empty letter δ.

Source: https://m.bulbapedia.bulbagarden.net/wiki/Δ_Delta_Species_(TCG)

Comments

The question asked about the set, not the special kind of Pokemon.

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Delta Species was both a set and a Special kind of Pokémon.  Based on the examples TY gave, I think that TY is talking about the Pokémon.

Answer 2

Pokémon TCG: EX Delta Species (Japanese: ホロンの研究塔 Holon Research Tower) is the name given to the eleventh main expansion of cards from the EX Series of the Pokémon Trading Card Game. It is the sixth main expansion from the PCG Era of the Pokémon Card Game in Japan. The set continues to feature Generation III Pokémon, Pokémon-ex, and Pokémon ☆ in the card game.

EX Delta Species is the name given to the eleventh main expansion of the EX Series of the Pokémon Trading Card Game. In Japan, it was released as Holon Research Tower, the sixth expansion in the Pokémon Card Game PCG Era. This set features Generation III Pokémon. The English expansion was released on October 31, 2005, while the Japanese expansion was released on October 28, 2005.

EX Delta Species introduced δ Delta Species, a type of Pokémon, and Holon's Pokémon, which could also double as Special Energy cards. The expansion was set in the Holon Research Tower, home of scientists who conduct research on Mew and strange new Pokémon. These Pokémon have been altered by a wave of electromagnetic radiation produced by an experiment gone awry at Holon labs. The result was a new species of Pokémon called the Delta Species. These new Pokémon possessed different types than their usual species.

Delta Species Pokémon had "δ Delta Species" between the name and HP, had double helix on the border of the artwork window, and the evolution box featured a δ design. Rare Holo cards for Delta Species Pokémon featured a plain "refractor" Holofoil on the Pokémon and the card border. Reverse Holofoil featured the same "refractor" Holofoil on the background of the artwork. Reverse Holofoil versions of the Rare Holo cards were updated to having gold foil HP text.

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