"Thunder Dragon" is an archetype of LIGHT and DARK Thunder monsters, used by Psychic Tendo in Yu-Gi-Oh! OCG Structures. Their first member was introduced in the Vol.7 Booster Pack, while their first support was introduced in Soul Fusion.
The general design and effect of each "Thunder Dragon" monster is based on and inspired by the original "Thunder Dragon", all of them being electrified dragons with a green, yellow, black or gray color scheme. "Thunder Dragon Titan" is especially influenced by the original "Thunder Dragon", which looks like a three-headed version of that monster, similar to the design of "Blue-Eyes Ultimate Dragon". "Thunder Dragondark" is a directly retrained version of the original "Thunder Dragon" as it has the same Type, Level, ATK, DEF, opposite Attribute, and similar effect of searching another copy of itself.
The archetype aims to provide card advantage and thin the Deck with various discarding and banishing effects. Almost all the "Thunder Dragon" monsters can discard themselves to activate a particular effect, generally revolving around searching another copy of itself or retrieving "Thunder Dragon" monsters in the Graveyard or that are banished, and a second effect that triggers when they are banished or sent from the Field to the Graveyard. In addition to this resource-providing mechanic, the Main Deck also contains a more straightforward, aggressive option, "Thunder Dragonduo", that can be Special Summoned by banishing 1 LIGHT and 1 DARK monster from the Graveyard, which can be used to trigger the effects of "Thunder Dragon" monsters, and enable Rank 8 plays for extra control. Also, after destroying a monster by battle, it can search any Thunder monster, which can give access to otherwise hard-to-search monsters, such as "Thunder King Rai-Oh" and "Denko Sekka".
The main bosses of the theme are the Fusions "Thunder Dragon Colossus" and "Thunder Dragon Titan". They have respectable stats and both of them can be Fusion Summoned with the traditional means (and the archetype has a Fusion Spell Card, "Thunder Dragon Fusion", that recycles Thunder monsters as materials) but also have an alternative Summoning condition that exempt the use of a Fusion Card or Effect. Their effects put more pressure on the opponent, by either serving as a one-sided "Mistake", or by destroying their cards on the field when a Thunder monster activates its effect in the hand, especially the Quick Effects of "Thunder Dragondark" and "Thunder Dragonmatrix". They also have strong protection, as they can banish cards from the Graveyard to prevent their destruction, which can be used to trigger the second effect of a "Thunder Dragon" monster(s).
Since the Deck rarely Normal Summons archetype monsters, generic Thunder monsters that help the Deck, and can be searched by "Thunder Dragonduo" and "Fusion", include "Batteryman Solar" and "Denko Sekka". The former can send a "Thunder Dragon" monster, mostly "Thunder Dragonroar", to the Graveyard, for it to be retrieved, banished or Special Summoned. It can also be used with its Token as Link Material for "Some Summer Summoner" or sometimes "Thunder Dragon Thunderstormech". The latter is a highly popular Side Deck choice that single-handedly locks down opposing backrow. Other popular Normal Summon choices include "Phantom Skyblaster" and "Armageddon Knight".
Due to the Deck being composed of LIGHT and DARK monsters that benefit from being banished, "Gold Sarcophagus" can used as a searcher/Summon from Deck by banishing "Dragondark" or "Dragonroar", however, it being Limited hurts this strategy. The Deck also has a large amount of synergy with the "Chaos" engine. Cards like "White Dragon Wyverburster" and "Chaos Dragon Levianeer" can be used to build combos and gain massive advantage, while cards like "Black Luster Soldier - Envoy of the Beginning" can be used to apply the finishing touch with high damage. In fact, "Fairy Tail - Snow" was judged to have so much synergy with this deck, it was made Forbidden.
Other common cards used in early builds were aimed at suppling Thunder monsters to the field for "Colossus" to be repeatedly Summoned in one turn, or for "Some Summer Summoner" to allow the Summon of "Colossus" before being itself turned into one. "Instant Fusion" can get a free Link Material out, or set up "Titan". "Brilliant Fusion" could achieve the same, with an extra "Foolish Burial" to boot, and it too was soon Limited. "Allure of Darkness" could be used for extra draws while banishing cards, and the aforementioned "Thunder Dragon Fusion" allowed for an easy "Titan" summon while recycling cards.
Current versions of the Deck are rarely played as "pure" builds, and often run engines like "Danger!", "Guardragon", "Chaos" and the "Curious, the Lightsworn Dominion"/"Knightmare Gryphon" combo, often multiple at once. With the realisation of the power of "Sekka's Light", few decks are running other Spells/Traps at all. The ones that are not using "Sekka's Light" are normally sticking with a small number of the classic consistency cards, while adding "The Melody of Awakening Dragon" to search "Chaos Dragon Levianeer" and sometimes "Darkest Diabolos, Lord of the Lair". With "Fusion" falling out of favour, "Titan" and "Dragonmatrix" are seeing very little current play, but "Thunder Dragon Colossus" remains not only a key end board enabler, but also a Rank 8 enabler with "Dragonduo". The current build considered presently optimal consists of combining a small amount of core archetype cards with the "Chaos" and "Danger!" engines to utilise the "Guardragon" engine and hence have easy access to powerful negation effects. A Rank 8 of choice is made, either "Number 22: Zombiestein" for a second negation or a monster able to Rank-Up into "Number 95: Galaxy-Eyes Dark Matter Dragon", sending "Amorphage Goliath" and "Arkbrave Dragon" to the GY in order to lock the opponent out of their Extra Deck. Finally, as the finishing touch, a single "Colossus" is left out, no longer the sole threat, but an important effect still to have.
Despite the Deck's sheer versatility, it still has many great weaknesses. Since the deck is so reliant on banishing cards, a well timed "Imperial Iron Wall", Artifact Lancea" or "Chaos Hunter" can completely shut the Deck down, and because it is also reliant on Special Summoning constantly to achieve swarming and field control, cards like "Vanity's Ruler", "Vanity's Fiend", and "Fossil Dyna Pachycephalo" can severely slow down the strategy.
The inherent protection of the "Thunder Dragon" Fusion monsters can also be bypassed by cards like "Invoked Raidjin", "Kaiju" monsters, "Castel, the Skyblaster Musketeer", "Book of Moon", "Cyberse Quantum Dragon", etc. Curiously, effects that banish them can also be helpful, since the Fusions themselves cannot be Summoned once they are banished and don't trigger any effect upon being banished.
Finally, all three of the "Drain" Continuous Trap Cards can put a complete seal on these Decks. In addition to the on-field effect negation of "Skill Drain", "Soul Drain" will prevent the triggering of effects of "Thunder Dragons" that hit the Graveyard or that are banished and "Mind Drain" prevents "Thunder Dragons" from activating their effects in the hand.