I'm not sure if this is known, but when you get a powerup you get a little bit of invincibility frames. You can use this in 6-Bowser to get through a burner and save time by not taking a hit from it (though it is a bit precise).

What burner?

The second one we normally damage boost through in bowser. It's basically tapping the raccoon suit earlier so that mario gets it right before he touches the burner.

Ah. I mean, yeah, that would be slightly faster if you do it right, but still it is kinda precise and it would save only around half a second.