Animation.CrossFade
CrossFade(animation: string, fadeLength: float = 0.3F, mode: PlayMode = PlayMode.StopSameLayer): void;
Description

Fades the animation with name animation in over a period of time seconds and fades other animations out.

If mode is PlayMode.StopSameLayer, animations in the same layer as animation will be faded out while animation is faded in. if mode is PlayMode.StopAll, all animations will be faded out while animation is faded in.

If the animation is not set to be looping it will be stopped and rewinded after playing.
	// Fade the walk cycle in and fade all other animations in the same layer out.
	// Complete the fade within 0.2 seconds.
	animation.CrossFade("Walk", 0.2);
Another example:
	// Makes a character contains a Run and Idle animation 
	// fade between them when the player wants to move
	function Update () {
		if (Mathf.Abs(Input.GetAxis("Vertical")) > 0.1)
			animation.CrossFade("Run");
		else
			animation.CrossFade("Idle");
	}