From Bulbapedia, the community-driven Pokémon encyclopedia.
The Holon Engine consists of several cards in the Pokémon Trading Card Game that work very well together and cause a deck to run smoothly and quickly when used. The strategy of the Holon Engine is to use Holon supporters to quickly burn through the player's deck and root out the cards they need to put together combos very early in the game (known as an Engine). The key card in the deck is Holon Transceiver, which allows a player to search their deck for any Supporter card with Holon in its name and add it to their hand.
Cards in the Holon Engine
Notable Decks That Use The Holon Engine
The Holon Engine became the dominant Trainer engine in the TCG, particularly after the introduction of Holon Adventurer in the EX Holon Phantoms set. As a result, components of the engine (Holon Transceiver especially) became highly valuable, making it difficult for players with limited resources to construct competitive decks. The high value for these cards has been listed by Play! Pokémon officials as a reason for the rotation of EX Delta Species out of the 2007-2008 Modified format.