LayerAnimation.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Playables;
using UnityEngine.Animations;

public class LayerAnimation : MonoBehaviour {

	PlayableGraph graph;
	AnimationMixerPlayable mixer;

	[SerializeField] AnimationClip runClip, face1Clip, face2Clip;
	[Range(0, 1)] public float weight;

	void Awake()
	{
		graph = PlayableGraph.Create ();
	}

	void Start()
	{
		// アニメーションをResourcesから取得し
		// AnimationClipPlayableを構築
		var runPlayable = AnimationClipPlayable.Create (graph, runClip);
		var face1Playable = AnimationClipPlayable.Create (graph, face1Clip);
		var face2Playable = AnimationClipPlayable.Create (graph, face2Clip);

		// 表情を二つ登録
		mixer = AnimationMixerPlayable.Create (graph, 2, true);
		mixer.ConnectInput (0, face1Playable, 0);
		mixer.ConnectInput (1, face2Playable, 0);

		// runPlayable（走るモーション）とmixer（表情）を合成
		var layer = AnimationLayerMixerPlayable.Create (graph, 2);
		layer.AddInput (runPlayable, 0, 1);
		layer.AddInput (mixer, 0, 1);

		// outputを生成して、出力先を自身のAnimatorに設定
		var output = AnimationPlayableOutput.Create (graph, "output", GetComponent<Animator>());

		// playableをoutputに流し込む
		output.SetSourcePlayable (layer);

		graph.Play ();
	}

	void Update()
	{
		mixer.SetInputWeight (0, weight);
		mixer.SetInputWeight (1, 1 - weight);
	}

	void OnDestroy()
	{
		graph.Destroy ();
	}
}