Coin Rush Star
From the Super Mario Wiki
The Coin Rush Star is an item that appears in Super Mario Run's Toad Rally mode. It is a blue star with silver eyes (which is inverted from the Super Star's colors). By collecting coins and performing certain moves, players can fill up a gauge in the top center of the screen. Once the gauge is filled up, the Coin Rush Star will appear from the meter and hover over the player for a few seconds, before dropping onto them and activating a Coin Rush for an amount of time. However, this does not make the affected character invincible. The Coin Rush's time can be increased when coins are collected and moves are performed.
During a Coin Rush, enemies will give twice as many coins when defeated, more coins and power-ups will come out of blocks, and coins will come out of pipes.
A Coin Rush can also be activated by collecting a Super Star; the Coin Rush will then last as long as the star does.