Double Tuning

Double Tuning (also known in some circles as Overtuning) 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 Red Nova Dragon.

Though Red Nova Dragon is the first to specifically say that it needs 2 Tuner Monsters, 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.

So far, the only monsters that require this method of Summoning are:Red Nova Dragon and Vairon Omega in the TCG/OCG