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To be Summoned, Synchro Monsters require Tuner monsters to be face-up on your field. When the total Level of the Tuner monster and any other face-up monsters on your field exactly matches the Level of the Synchro Monster you wish to Summon (no more or less), by sending them to the Graveyard, you can Synchro Summon the Synchro Monster. The monsters used are referred to as Synchro Material Monsters.
Some Synchro Monsters require a specific Tuner monster in order to be Synchro Summoned (such as "Moon Dragon Quilla"), monsters of a particular Type ("Driven Daredevil"), Attribute ("Vylon Sigma") or even Archetype ("Thor, Lord of the Aesir") as Material Monsters, but many do not, so they can be in just about any Extra Deck. Thus, Synchro Monsters are generally more splashable in decks than Fusion and Ritual Monsters, as many require just a single Tuner and another monster to Summon them, and almost any Deck can run a few Tuners. Ritual and Fusion monsters on the other hand, generally require certain specific monsters to be on your field or in your Graveyard to Summon them, along with the proper Spell card.
Strategically speaking, Synchro Monsters allow for a large amount of rapid power to be Summoned with relative ease and speed. Most of them have very potent effects in addition to their ease in Summoning. They do not necessarily always have card advantage over Fusion Monsters, because a player might use up as many cards getting all of the Material Monsters on the field to perform a Synchro Summon in one turn, but they have the advantage of increased flexibility and speed over Fusion Monsters due to the fact that many of them have very non-specific requirements for them to be Summoned, so a player with a Tuner monster and a non-Tuner monster on the field will always have one or more options for Summoning, especially if card effects that allow Levels to be changed are used.
Some Synchro Monsters require 2 or more non-Tuner monsters to be summoned, such as "Mist Wurm" or "Ally of Justice Decisive Armor". In that case, you will need at least 3 monsters on the field. Also, while generally most of the Synchro Monsters require exactly 1 Tuner to be summoned, "Red Nova Dragon" and "Vylon Omega" require 2. Additionally, Token Monsters may be used as non-Tuner monsters for a Synchro Summon, because they still have Levels and Synchro Monsters do not require the Tokens to be there when the Synchro Monster is summoned.
Because Synchro Monsters belong in the Extra Deck, they return there whenever they would be returned to the hand or Main Deck, like Fusion Monsters before. Also, like Fusion Monsters, they cannot be Special Summoned from the Graveyard if they were not properly Synchro Summoned first. As with all Special Summoning certain criteria must be met.
There are also two special types of Synchro monsters: Tuner and Accel Synchro monsters. The first are Synchro monsters that are Tuner monsters, simultaneously. Usually, they have effects that tend to ease a Synchro Summon (either by allowing you to Synchro Summon during your opponent's turn, or by managing their own level and restricting Special Summons other than Synchro Summons). They are generally used to perform the Synchro Summon of the latter, that is a kind of Synchro Monster that specifically needs all of its Synchro Materials to be Synchro monsters; their level is always high and they have powerful effects, ranging from negating an effect to attacking multiple times (AND negating effects).
However, whilst Synchro Monsters still have not appeared in the ZEXAL anime or manga, additional support for Synchro Monsters still appear on occasion in the TCG although the primary focus of all new products is Xyz Monsters. The TCG version of the booster packs Generation Force, Order of Chaos, Photon Shockwave and Cosmo Blazer all included 1-3 new Synchro Monsters despite primarily containing Xyz Monsters. Synchro Monsters also have been on occassion released in the 2012 Collectors Tins as promo cards and new Synchros were still released in several Hidden Arsenal sets, Hidden Arsenal 5: Steelswarm Invasion and Hidden Arsenal 6: Omega Xyz. The latest addition in Gold Series, Gold Series: Haunted Mine contained reprinted Synchro Monsters as well. The 2012 Premium Collection Tin also included 3 new Synchro Monsters, and several Synchro Monsters were reprinted in the 2013 Collectors Tins. Judgment of the Light, however, marks the first time since Xyz Monsters came into the game that Synchro Monsters gained much support and new monsters, featuring 8 new Synchros, about the same number released per set during the Yu-Gi-Oh! 5D's era of the TCG. One of the newest Structure Decks, Structure Deck: Saga of Blue-Eyes White Dragon features a "Blue-Eyes White Dragon" Synchro Counterpart ("Azure-Eyed Silver Dragon"). Shadow Specters and Legacy of the Valiant released 4 and 3 Synchro Monsters respectively, including brand new, splashable and generic ones, such as "Giganticastle" and "Leo, the Keeper of the Sacred Tree", TCG-exclusives, like "Powered Inzektron", and Synchro monsters that only existed in the OCG, such as "Celestial Wolf Lord, Blue Sirius".
Role in the anime
Synchro Monsters have the power to manipulate Ener-D, allowing humans to accelerate their evolution. It was a vital part of the plot of Yu-Gi-Oh! 5D's and the series antagonists' intentions. However, it was never explained exactly how Synchro Monsters obtained this ability.
A possible theory is linked to the statement that Synchro Monsters are the "symbols of human evolution". This could be the case when one considers how intricately linked humanity is to Duel Monsters and Ener-D. It is stated by Jakob that man's excessive use of Synchros caused Ener-D to spin faster, producing more energy and thus accelerating human evolution. It could be that this energy is fueling human evolution because of Synchros, the "symbols of human evolution". Humanity expresses its subconscious desire for evolution by obsessing over and excessively using Synchro Monsters.
- Machine-Type monsters are currently the most diverse monsters by Level, as they have Synchro Monsters that are Levels 2, 3, 4, 5, 6, 7, 8, 9, 10, and 12.
- They are followed by the Dragon-Type, that has Level 4, 5, 6, 7, 8, 9, 10, 11 and 12 Synchro Monsters.
- The only 3 Zombie-Type Synchro Monsters ("Revived King Ha Des", "Doomkaiser Dragon" and "Archfiend Zombie-Skull") are zombified versions of pre-existing monsters and all require "Plaguespreader Zombie" to be the Tuner monster.
- They are also all Level 6.
- "Star Eater" is the only Synchro Monster whose Synchro Summon cannot be negated, and the only one who prevents the activation of cards or effects when it is Synchro Summoned.
- Also, it is, so far, the only Level 11 Synchro Monster.
- "XX-Saber Gottoms" is the only Synchro monster that can be Summoned with all of its Synchro Materials being Tuner monsters, as it doesn't have the sentence "non-Tuner monster(s)".
- "Sea Dragon Lord Gishilnodon" is the only Synchro Monster who specifies the Level of the non-Tuner monster required for its Synchro Summon.
- "T.G. Recipro Dragonfly" is currently the only Level 2 Synchro Monster that is not a Tuner Monster.