"T.G.", short for "Tech Genus" (ＴＧTekkujīnasu) is an archetype used by Antinomy in Yu-Gi-Oh! 5D's. They are all bionic in appearance to reference the identity of their user. They made their debut in Extreme Victory. In the Japanese anime, each of them has a code in their name which references their Type, followed by a number. This includes their status as they have X's at the end of their names to indicate their evolution of Synchro Monsters:
The real life version of the "T.G." cards consist of monsters who can "replace" themselves with different monsters when they're destroyed. Most of the non-Synchro Monsters search for other "T.G." monsters besides ones that share their name (for example, a "T.G. Warwolf" can search for any "T.G." monster besides "T.G. Warwolf"), while all of the Synchro Monsters (except "T.G. Blade Blaster") draw cards or Summon monsters.
Despite their bionic appearance and names, the only existing Machine-Type "T.G." monsters are Accel Synchro Monsters. All "T.G." supporting Spell and Trap Cards have an initialism in their names.
This archetype also excels at long, drawn-out Duels (a.k.a., "grind games"). A player can wear down their opponent's resources over time, while maintaining his/her own, due to the immense search and draw power of the T.G. cards.
"T.G. Striker", "T.G. Warwolf", and "T.G. Catapult Dragon" are the best cards to swarm with; the first two have easy Summoning requirements while "Catapult Dragon" can Summon more monsters and give "Warwolf" an opportunity to be Summoned by its effect. At the very least, in case you cannot Synchro Summon, you can build a defense and let your opponent destroy them, giving you plenty of cards to add to your hand at the End Phase.
"Mischief of the Yokai" can be used offensively or defensively. Since the non-Synchro Monsters are for Synchro Summoning Level 5 Synchro Monsters, using "Mischief" reduces the Levels of "Striker", "Warwolf", and "Catapult Dragon" to 1 without any drawback to "T.G. Blade Blaster", since it will most likely be on the field first.
"Star Changer" works similarly, allowing greater flexibility in Synchro Summoning, or potentially thwarting an opponent's Synchro or (especially) Xyz Summon.
Also, since the "T.G." cards share the ability to search once they are destroyed, support cards such as "Kuraz the Light Monarch" and "Needle Ceiling" can be used with little or no drawbacks. While the effect of "Kuraz" might seem too good to pass up on your own cards, remember that you can use it selectively: for example, you can choose to destroy your opponent's "Legendary Six Samurai - Shi En" and not target any of their other monsters. Additionally, mass-destruction staples like "Dark Hole", "Torrential Tribute", and "Black Rose Dragon" become even more effective, as they can be used with little to no drawback for the player.
"Plaguespreader Zombie" can also be used in this Deck to accelerate the rate of "Synchro Summon". "Debris Dragon" can revive "T.G. Cyber Magician" and other 500 ATK monsters in your Graveyard, while also triggering "T.G. Warwolf" in your hand. Cards like "Gravity Collapse" (negates a Summon and destroys the monster making the opponent unable to Summon more monsters for the rest of the turn by Tributing a Synchro Monster), "Synchro Material" ("steals" an opponent's monster that you can use to Synchro Summon), "Safe Zone" (protects 1 of your monsters from any kind of destruction and targeting effects by giving up direct attacks with the monster you are protecting with it) and specially, "Inferno Reckless Summon" (summons 1 or 2 more copies of a T.G. monster from your graveyard, hand or Deck when you special summoned one T.G. monster which makes the combo even better if you don't use the spare monsters special summoned by this effect and let them be destroyed to search the Deck at the end phase), are a staple in this Deck to keep the opponent under constant pressure and control even if they use a fast and powerful Archetype like the "Six Samurai" or to some extent, "Blackwings".
Since this archetype is one of the most Synchro-focused archetypes, rivaling Yusei-themed and Inca Decks, all anti-Synchro support ("Discord", "Synchro Control", "Greed Grado", "Meklords", "Shiny Black "C"", etc.) can kill the Deck, in addition to all the typical Anti-Meta strategies that most Decks fall prey to. "Dimensional Barrier" can prevent you from Synchro Summoning for a turn. "Soul Drain" completely turns off almost all of your "T.G." monsters, preventing you from activating your Graveyard effects to draw, Special Summon, or search. None of the non-Synchro Monsters provide any offensive capabilities, barring "Rush Rhino" with "TGX300" on the field. "Thunder King Rai-Oh" and "Mistake" can also stop their searching. Use "TG1-EM1" or "Creature Swap" to take control of your opponent's monster when you don't have strong attack power. Also, nearly all monsters have effects that ease the Synchro Summons while wreaking havoc on the player's hand. Therefore, field clearing becomes even more important so protect your monsters (especially "T.G. Hyper Librarian" with "Starlight Road" or "My Body as a Shield". You can also run multiple copies of "TGX3-DX2", due to the rate at which the T.G. monsters are Summoned, and - consequently - sent to the Graveyard to replenish your hand and recycle your T.G. monsters.
Additionally, the "T.G." archetype is extremely weak to many common Side-Deck cards, such as "Gozen Match", "Vanity's Emptiness", and "Mistake". "Rivalry of Warlords" deserves a special mention, because it completely shuts down the deck, due to the T.G. monsters consisting of entirely different Types. Because of this, one should build their Main/Side deck with these threats in mind. "TGX1-HL" is a great card that T.G.'s have at their disposal, which is functionally the same as "Mystical Space Typhoon", should one need additional Spell/Trap removal.