1. Command mercenaries to move : When you are in battle, the whistle can be used to command mercenaries to follow you or your pets to move freely.
2. Gather mercenaries : The whistle can gather mercenaries together to reduce the chance of being hit by enemy bullets. This can maintain the team's blood line and has a great practical effect.
3. Equipment upgrade : When you enable commander mode, you can upgrade the pet weapon to gold quality by embedding the whistle on it.
In the starting room of level 1-1 of the game Soul Knight, after opening the treasure chest, you will definitely get the red weapon - the whistle.
The above content is a detailed answer to the function of the Vitality Knight Whistle and how to obtain it. I hope it will be helpful to you.