Super Saiyan 11 is a form that only Goku has achieved which surpasses Super Saiyan 10. In this form, Goku's
eyebrows disappear and the hair looks like it does as a Super Saiyan 3 except red. His gi also turns grey with a red shirt underneath and he has tattoos on his face.
How Goku became a Super Saiyan 11
One day, an evil cult stole the Dragon Balls and wished Xicor, the evil son of Goku back to life (Xicor was killed fighting Goku). He was ten times stronger this time and had gone all the way up to Super Saiyan 10. In order to get revenge against Goku, he summoned all the evil in the universe into one army and attacked Earth. Goku, Vegeta, Gohan, and Trunks went into space to stop the army of evil but it was too powerful. Vegeta went Super Saiyan 10 but was defeated by the powerful warriors, Gohan was defeated as a Super Saiyan 7, and Trunks was defeated as a Super Saiyan 5. Goku was the last one standing and was badly injured, Vegeta, Trunks, and Gohan were barely conscious. They gave their remaining energy to Goku and Goku ascended into a Super Saiyan 11 and destroyed the entire army with a Spirit Bomb. Then, Goku defeated Xicor who was a Super Saiyan 10. After this, Goku teleported to Earth with Vegeta, Trunks, and Gohan who was healed by Dende.