This can auto activate if the player was caught by a ] and bitten.Also, with the third hit, Titan Eren can kill 1-3 titans at once. Remember, if it is a larger titan, you don't HAVE to land the third hit on it, the third punch will automatically kill titans if it makes contact with the titans, the most effective way to use this is to start attacking titans from a distance away, this can also allow you to kill the smaller titans with the third punch however it isn't a smart choice as you can miss and the kick can kill them faster.
When in Titan Eren mode, try to use your time as efficiently as possible. This has two main focuses: To act as a safety net in case you get caught, or to act as a desperate measure. Players will run at 64.5 feet per second, and cannot dodge. A few seconds after the titan body will evaporate. After 15 seconds are over Eren will tire and exit the titan. They can punch and kick other titans to kill them and the titan form lasts for 15 seconds. After this the player is able to control the titan. Upon activation, the player will turn into a titan with a flash of yellow light.