Bubbles serve as extra lives to help you get through both Tour and Toad Rally modes in Super Mario Run. Even better, they let you rewind back to pick up any items that were missed. But unbeknownst to many, you can activate a bubble even if you haven't gotten knocked out yet.
This feature is great for moving back in a level to get another chance at picking up any special coins you may have missed. And the best part of all, manually triggering a bubble will preserve all the coins you collected and even keep any power-ups intact.
To use a bubble manually, simply tap on the bubble icon in between the pause button and clock, and Mario will automatically be transported via bubble to any previous point of the current stage you're running through.
You'll still need to be careful when employing a bubble, because rules still apply with regards to time constraints and losing a life. In other words, try not to let the bubble take you too far back, because you'll still need to finish the level before time expires. Otherwise, you'd have to play through the stage and collect any special coins all over again.
But once you've learned to master the bubble, it'll be a lot easier to collect all of the special purple coins in every level, which, in turn, will make it easier to earn extra Toad Rally Tickets.