Use the Influence Helper to soft select vertices and apply proximity-based falloffs to effects. 
  

Influence Helper shown selecting vertices to create an effect used in an animation of a cartoon train. The inner gizmo is applying maximum influence to all vertices inside while the outer gizmo gradually tapers the effect off.
 
Interface
 
		 
		
 
		
- On 
			 
- Enables the helper's effect. 
			 
- Near 
			 
- Sets the starting distance of the effect. Click the color swatch to select a new color for the associated gizmo, if desired. 
			 
- Show 
			 
- Displays the Near gizmo in the viewport. 
			 
- Far 
			 
- Sets the farthest distance of the effect. Click the color swatch to select a new color for the associated gizmo, if desired. 
			 
- Show 
			 
- Displays the Far gizmo in the viewport. 
			 
- Falloff 
			 
- Sets the type of falloff curve: either Linear, Smooth or Smoother. 
			 
- Invert 
			 
- Inverts the falloff value. 
			 
- Apply Bias 
			 
- Applies a bias amount to the falloff curve. 
			 
- Amount 
			 
-  Sets the amount of bias to apply to the falloff curve. 
			 
- Only When Selected 
			 
-  When enabled, only applies the bias to targets that fall within the selection area.