"Chaos Emperor Dragon - Envoy of the End" was the first of this trio to be sent to the Forbidden list, in September 2004. "Chaos Emperor Dragon - Envoy of the End" is known as one of, if not THE most broken card of all time. This card helped form the Yata-Garasu Lockdown, a very deadly and broken Deck, by using "Sangan" or "Witch of the Black Forest" with its effect to bring "Yata-Garasu" into your hand. The finishing blow required you to Summon, attack, and Lockdown your opponent, leaving them with no cards in their hand or on their field and leaving them unable to draw additional cards.
"Chaos" still continued to dominate the Metagame for the next 12 months. 2005 saw a "Chaos Phoenix" Deck using "Black Luster Soldier - Envoy of the Beginning" and "Sacred Phoenix of Nephthys" which proceeded to win the 2005 World Championship. This showed people that "Black Luster Soldier - Envoy of the Beginning", even if Limited to 1, was still far too powerful to be allowed to be used in Advanced Format. In September 2005, "Black Luster Soldier - Envoy of the Beginning" was Forbidden, but is now back with the release September 2011 ban list.
The next 12 months saw the emergence of the strongest "Chaos" Metagame since Invasion of Chaos. This style of "Chaos" revolved around "Chaos Sorcerer", which was still Unlimited, combined with the flexibility and power of the "Monarchs". "Chaos Sorcerer" was eventually Forbidden in September 2006.
The "Chaos" ideal was left untouched until the release of Force of the Breaker, where the "Chaos" era was reborn with the "Sky Scourges", two monsters whose effects were based on "Chaos Emperor Dragon - Envoy of the End" and "Black Luster Soldier - Envoy of the Beginning", with a third that was able to "choose" between the effects of "Jinzo" or "Spell Canceller". Neither of the new "Chaos" replacements made much of an impact, and have long since been condemned to the unused Card Pool on account of their Summoning Conditions being unworkable and situational. More recently, a Deck based around "Sky Scourge Norleras" and "Phantom of Chaos" has been seeing more play after it topped a regional (September).
A new Synchro Monster, "Chaos Goddess", was released in The Shining Darkness. It is capable of Summoning Level 5 or higher DARK monsters to the field by discarding a LIGHT monster from the hand. However, the fact that it requires a LIGHT Tuner and two non-Tuner DARK monsters makes it tricky to get out.
"Chaos" monsters have also the rare honor of being one of the few cards ever mentioned to be banned in tournament plays due to their rarity and powerful effects, this is also mentioned with other cards such as "Gate Blocker" and "Gate Blocker 2" which had been banned in official Turbo Duels in Yu-Gi-Oh! 5D's.
Chaos Lockdown (Traditional Format only)
While this Deck is dead in every regard due to the banning of "Yata-Garasu", "Sangan" and "Chaos Emperor Dragon - Envoy of the End", it was the most potent Deck in the Metagame. It focused on using "Chaos Emperor Dragon" to clear the field and use "Sangan" or "Witch of the Black Forest" to search for "Yata-Garasu", winning the game. At the moment this Deck is only capable of being used in Traditional Format.
This focuses on milling the Deck to use "Lightsworn" monsters and Summon "Judgment Dragon" while at the same time placing DARK monsters in the Graveyard in order to Summon "Dark Armed Dragon". Since the milling effect can place vital monsters in the Graveyard, this makes use of Graveyard control cards such as "Monster Reincarnation", "Necro Gardna" and "Pot of Avarice" to make sure that they get the cards required in their hand and Graveyard. With the high amounts of DARK and LIGHT monsters being sent to the Graveyard, "Chaos Sorcerer" can work very well in this Deck. So can "Chaos Necromancer" because you're always dumping cards and the more cards that are in your Graveyard, the more powerful it gets. "Tragoedia" is another important monster for the Deck, offering protection from OTK's, versatility as a Synchro Material and the potential to become a huge beatstick, provided the player has enough cards in their hand.