Tuner (monster)[Notes 2]
Tuner monsters (Japanese: チューナー Chūnā, "Tuner") are monsters with "Tuner" listed on the Type line. They are required for the Synchro Summon of a Synchro Monster. Normal, Effect, Fusion, Ritual, Pendulum, and Synchro Monsters themselves can all be Tuner monsters; additionally, some card effects can treat non-Tuner monsters as Tuners. Because Tuner is not an Ability, Tuner monsters can also have an Ability, such as Flip or Union. Special Summon Monsters can also be Tuner monsters.
To perform a Synchro Summon, the player sends monsters they control (including a Tuner monster) to the Graveyard whose total Level is exactly equal to that of a Synchro Monster in their Extra Deck, then they Synchro Summon that Synchro Monster. Usually, Synchro Summons require exactly 1 Tuner monster, but some Synchro Monsters allow or require multiple Tuner monsters (methods referred to as Double Tuning or Triple Tuning).
Some Synchro Monsters require a specific Tuner monster to be used ("Sun Dragon Inti"), or a Tuner of a specific Type ("Trident Dragion"), Attribute ("Dragocytos Corrupted Nethersoul Dragon"), or archetype ("Blackwing Tamer - Obsidian Hawk Joe"), etc. Likewise, some Tuners can only be used as Synchro Material for a limited set of Synchro Monsters, such as "Brotherhood of the Fire Fist - Spirit", "Mystic Macrocarpa Seed", and "Scrap Soldier".
There are also Tuner Synchro Monsters, Synchro Monsters that are themselves Tuners. They tend to have effects that make further Synchro Summons easier, such as by manipulating their own Level ("Phonon Pulse Dragon"), allowing its controller to Synchro Summon during the opponent's turn ("T.G. Wonder Magician"), or having effects that activate when used as a Synchro Material ("Puralis, the Purple Pyrotile"). In the anime, Tuner Synchro Monsters are notably required for Accel Synchro Monsters, such as "Shooting Star Dragon".
Generally speaking, Tuner monsters are often low in Level, usually ranging from Level 1 to 3. A number of Level 4 Tuner monsters exist, although older Level 4 Tuner monsters often have negative effects or conditions that limit their use. The first Level 4 Normal Tuner monster, "Angel Trumpeter", was not released until 2016, eight years after the debut of Tuner and Synchro monsters.
Due to Synchro Summoning summing Levels, there are not many Level 5 or higher Tuner monsters. The Level 5 and higher Tuner monsters that do exist often change Levels ("Flower Cardian Willow with Calligrapher", "Mare Mare") or have an alternative playstyle ("Ursarctic Megapolar").
Many Tuner monsters have effects that assist in performing a Synchro Summon, such as by Special Summoning another monster ("Deep Sea Diva", "Masked Chameleon"), Special Summoning themselves when a condition is met ("Lady of the Lake", "Fishborg Archer"), or managing the Level, Type, or Attribute of monsters ("Delta Flyer", "Genomix Fighter", and "Genex Ally Chemistrer", respectively). One Tuner monster, "Phantom King Hydride", can treat itself as a non-Tuner monster for a Synchro Summon.
As implied by the name, several Tuner monsters and their designs have ties to sound, like "Frequency Magician", "Phonon Pulse Dragon", and the "Resonator" monsters. Many Tuner support cards have references to music or wavelengths, like "Natural Tune", "Resonator Call", and "Tuning".
When they were first released, Tuner Pendulum Monsters tend to have an effect or condition that restricts how they can be used as a Synchro Material and/or causes them to become difficult to retrieve if used as Synchro Material (such as by banishing themselves or shuffling themselves into the Deck). This was because otherwise they could easily be Pendulum Summoned again the next turn, to be used as Synchro Material again.
Due to New Master Rule limiting the ability to Pendulum Summon from the Extra Deck, Tuner Pendulum Monsters have become less restricted. Restrictions often only apply if the Tuner Pendulum Monster was Summoned from the Extra Deck or, in the case of Normal Tuner Pendulum Monsters, do not have any restrictions at all.