One stroke painting is such an impressive skill that it's unbelievable even when you see it happen. These artists from Kousyuuya in Nikko, Japan have been mastering their craft for over four generations. The amount of detail they can put out with one stroke is just unreal.
The GIF above sums it up but if you want to see the amount of effort put in this one stroke, just watch the video below. It takes an insane amount of skill.
The detail of the dragon comes with other brushes but the main body is all from one stroke.