Super Saiyan 6 is the 6th evolution of Saiyans and one of the most limit-breaking forms that can possibly be achieved.
Super Saiyan 6 is achieved with immense training and burns through stamina at an extreme rate. It is easily one of the most difficult forms for a Saiyan to achieve. The warriors who have achieved this form put themselves through training that cannot be compared.
Currently this form has only been seen in Universe 13 and the Universal Tournament.
List of Warriors who have achieved Super Saiyan 6.
Ryu
Resurken
Rinder