In the anime
Visually in both series, this Summoning is represented with the chosen Tuner monsters transforming into rings of fire in place of the usual green rings found in standard Synchro Summoning.
Optional use of multiple Tuner monsters
While "Hot Red Dragon Archfiend King Calamity", "Red Nova Dragon", "Tyrant Red Dragon Archfiend", and "Vylon Omega" are the only Synchro Monsters that require 2 Tuner monsters, Double Tuning is possible with other monsters that do not specify that the monsters after the required Tuner must be non-Tuners.
"XX-Saber Gottoms" must be Synchro Summoned using a Tuner and EARTH monsters, but it does not specify that the EARTH monsters must be non-Tuners. Therefore, up to 5 Tuner monsters can be used for its Synchro Summon.
If a specifically named Synchro Material Monster is treated as a Tuner monster, it can be used for the Synchro Summon and result in there being 2 or more Tuner monsters used. For example, if "Stardust Dragon" is treated as a Tuner monster, it can be used as a Synchro Material for the Synchro Summon of "Majestic Star Dragon" or "Shooting Star Dragon" in addition to the necessary Tuner monster. If "Red Dragon Archfiend" is treated as a Tuner monster, "Red Nova Dragon" can be Synchro Summoned using 3 Tuner monsters.
List of monsters that require Double Tuning
So far, the only monsters that require this method of Summoning are:
|Hot Red Dragon Archfiend King Calamity||琰魔竜王 レッド・デーモン・カラミティ||12||DARK||Dragon||4,000||3,500|
|Red Nova Dragon||スカーレッド・ノヴァ・ドラゴン||12||DARK||Dragon||3,500||3,000|
|Tyrant Red Dragon Archfiend||レッド・デーモンズ・ドラゴン・タイラント||10||DARK||Dragon||3,500||3,000|