"Genex" (ジェネクス Jenekusu) is an archetype of mostly Machine monsters with various Attributes (primarily DARK) that exist in the TCG/OCG. Most of their effects involves adding monsters from the Deck to the hand and Special Summon them, as well as using "Genex Controller" with low-Level monsters of the four basic Attributes for Synchro Summon. The name of "Genex" Synchro Monsters takes after sources of energy such as hydroelectric, geothermal, solar, etc.
"Genex" monsters were introduced in "Duel Terminal - Invasion of Worms!!". Two more sub-archetypes were added in "Justice Strikes Back!!", "Champion of Chaos!!" and "Charge of the Genex!!": "R-Genex" and "Genex Ally", respectively.
"Genex Controller" appears as a character in Yu-Gi-Oh! 5D's World Championship 2009: Stardust Accelerator, and in Yu-Gi-Oh! 5D's World Championship 2010: Reverse of Arcadia, both "Locomotion R-Genex" and "Genex Ally Bellflame" appears in 2010, and "Genex Ally Axel" appears in Yu-Gi-Oh! 5D's World Championship 2011: Over the Nexus.
In terms of viability, the "Genex" archetype suffers from having purely monsters and no Spell/Trap support. While the main archetype mostly revolves around the use of "Genex Controller" to achieve various effects and perform Synchro Summons of the Extra Deck monsters, "R-Genex" focuses on assisting the Special Summon of Genex and "R-Genex" monsters for swarming, and "Genex Ally" focuses on manipulating the six attributes to achieve different effects.