Can SSJ4 Goku do a 20x Kaio-ken 10x Kamehameha?
Theoretically yes. He can do such a feat but it may kill him. 20x kaio-ken at ssj4 may destroy his body because of too much strain and power. This may also be the most powerful attack ever done, more powerful than the spirit bomb used to defeat omega shenron, if it really happened. It would be too much to think if Goku did an instant 20x kaio-ken 10x kamehameha at ssj4. That’s a combination of Instant transmission, 20x kaio-ken, and 10x kamehameha at ssj4.