The auto-battle feature allows you to have the game play by itself in Story missions battles for you! Once this feature is unlocked in Chapter 2, you can use it across all game modes (Story, Portal, Hawkins National Lab, Hellfire Club and Club Boss).
The auto-battle feature must be manually turned on with the start of each mission. To turn it on, tap the icon with two arrows in the top-right of the screen, just under the Flee button.
While useful for quickly progressing through the game, have in mind that some character abilities may be skipped in auto-battle mode. This applies to abilities that require you to make a decision — such as tapping and selecting a target or a die, or abilities that cannot be fulfilled at that moment — such as a healing ability when there’s no character to heal.
The auto-battle feature can be turned on and off as often as you want when in battle. It is up to you to use it wisely!