How do I trigger a Fever?

I noticed that when I pick a stage with my balloon, sometimes I get Fever, which allows me to go to areas with more stars.

Is there a way to trigger a Fever, or is it random? If it isn't random, how do I do it?

Solution 1:

Unfortunately, Fever is a completely random event.

The method of getting this is completely random, but there is a way to see if you're likely to get one. When you return from a previous stage, if there is a rainbow around your balloon in the cutscene, then you have a chance of getting Fever in your next stage, so be sure to make sure you know what stage you're selecting first.

Source: Serebii