The Dragon aka Sumotori Sensei is the fifth challenge and the first boss you encounter in the Winterfest DLC. It's a guy in a fat sumo suit. This challenge is probably the hardest one of all the 21 challenges.
Keep to the left. As far left as possible. That way there are a lot less totems to avoid. Sharp turns (both thumbsticks) make it easier to dodge the spawning totems. It will make you go slower but that's not really a problem. You don't have to be very fast to beat the guy. There is some leeway, even room for error.
See this video: