Double Tuning
Double Tuning is a method of Summoning Synchro Monsters using two Tuner Monsters rather than the usual one. This type of Synchro Summoning was first seen in Episode 113, used by Jack Atlas when he summoned Scar-Red Nova Dragon.
Though Scar-Red Nova Dragon is the first to specifically say that it needs 2 Tuner Monster, Double Tuning is possible with XX-Saber Gottoms when the EARTH monster(s) is also a Tuner Monster, but also Gottoms can be Summoned with any number of Tuner Monsters, provided they are EARTH.
Example
