The prime reason Metagross and Gorebyss were used in tandem was not for any inherent synergy in their effects, but in their typing. Together, they covered each other's Weaknesses and were able to take advantage of the Weaknesses of many other attackers of the era. Furthermore, each were capable of abusing Double Rainbow Energy to attack faster. As a dual Psychic/Metal-type, Metagross attacked for increased damage against popular Pokémon such as Walrein, Gardevoir ex, and Crobat (a frequent fixture in other Gorebyss decks). Metagross was weak to Fire, which was problematic due to the prevalence of Blaziken and Blaziken ex in the metagame (although the latter was also weak to Metagross itself), so Gorebyss served to counter Fire-types.
Although the primary goal of the deck was simple (attack as soon and as often as possible with either Metagross or Gorebyss, depending on the matchup), there was no clear-cut path on how to optimally accomplish this. A particular area of contention involved which Beldum to use. There were three options: Beldum (EX Hidden Legends 28), Beldum (EX Hidden Legends 29), and Beldum (EX Hidden Legends 54). The first had a Poké-BODY, Levitate, that granted it free retreat if it had any Energy attached. This was useful both in tandem with a starter Pokémon such as Dunsparce or Jirachi, as it provides a way to easily retreat Beldum and attack with a preferable Pokémon instead. Levitate was particularly useful given Metagross's Metal JuncturePoké-POWER, which could be used to move Metal Energy used to retreat off of Beldum and onto an attacking Metagross later in the game. The second Beldum, numbered 29, had a Poké-POWER called Magnetic Call that allowed the user to flip a coin once during their turn, and (upon a successful flip) search their deck for another Beldum and place it onto the Bench. The third Beldum, numbered 54, had a Call for Family attack for a cost of , which searched the deck for one Basic Pokémon and placed it onto the user's Bench. Unlike the other two Beldum, which were Metal-type, this Beldum was Psychic-type and thus not weak to Fire, giving it greater staying power against Blaziken-based decks.
MetaByss lists also often differed in their choice of starting Pokémon. Like most decks of the era, MetaByss often relied on Dunsparce's Strike and Run attack to set up, but a more aggressive player may have felt that Dunsparce was redundant when included in a deck already running either the Magnetic Call or Call for Family Beldum and opted to run Jirachi instead. The list below runs both, making it less consistent but more versatile.
Metagross - Metagross was one of the deck's two main attackers. Pending favorable coin flips, it was capable of doing large amounts of damage with its Squared Attack, as well as abusing the effects of both Special Metal Energy and Double Rainbow Energy.
Dunsparce - Dunsparce was the deck's ideal starter Pokémon. With its Strike and Run attack, Dunsparce could instantly give the player a strong setup; most decks of the time relied on Dunsparce early in the game.
Special Metal Energy - Special Metal Energy reduced 10 damage done by attacks to the Metal-type Pokémon it was attached to. Thus, a Metagross with one or more Metal Energy attached was difficult for many decks to Knock Out in one or even two attacks.
Double Rainbow Energy - Double Rainbow Energy provided a way to power up either Metagross's Metal Juncture or Gorebyss's Mystic Water in fewer turns than usual.
The deck list appearing below is not official; it is meant to represent an average build of the archetype, not specifically constructed for any regional metagame. Being that this is merely an archetype, a player may wish to change any part of this deck when building his or her own version. The list shown assumes an Expedition through EX Hidden Legends format. Potential later additions may be listed in the Possible tech cards section.
The following cards were often used in MetaByss in place of certain cards included in the above list.
Metagross ex - While Metagross ex was incapable of hitting Psychic-weak Pokémon like its non-ex counterpart, and gave up two Prize Cards when Knocked Out, some MetaByss players chose to include it as a way to deal surefire damage without the coin flips the non-ex Metagross required to attack.
Magnetic Storm - Although Psychic-type Resistances were uncommon at the time, a MetaByss player playing in an unusual metagame may have wished to include one or two copies of Magnetic Storm.
Ancient Tomb - Ancient Tomb, which negated the Weaknesses of each Pokémon in play, may seem counterintuitive given MetaByss' focus on taking advantage of opposing Weaknesses. However, it was useful against the Aqua archetype, which saw occasional play, and made it safer to use Metagross as an attacker in a pinch against Fire-type decks.
Mr. Briney's Compassion - For many decks, a Metagross with one or more Special Metal Energy attached could prove difficult to Knock Out in one or even two attacks. Mr. Briney's Compassion allowed the MetaByss player to pick up a damaged Metagross, both preventing the opponent from taking a Prize card and preserving the Special Metal Energy.
Professor Oak's Research - Some players preferred utilizing Professor Oak's Research over Copycat and/or Professor Birch.