概要

下記のスクリプトを使用することで、
このようなシンプルな待機アニメーションを実装できます

using UnityEngine;

public class IdleAnim : MonoBehaviour
{
    public float min = 0.95f;
    public float max = 1.05f;
    public float speed = 2;

    private float time;

    private void Update()
    {
        time += Time.deltaTime;
        var t = time * speed;
        var amount = Mathf.PingPong( t, 1 );
        var x = OutQuad( amount, 1, max, min );
        var y = OutQuad( 1 - amount, 1, max, min );
        var scale = transform.localScale;
        scale.x = x;
        scale.y = y;
        transform.localScale = scale;
    }

    private float OutQuad( float t, float total, float max, float min )
    {
        max -= min;
        t /= total;
        return -max * t * ( t - 2 ) + min;
    }
}

参考ツイート

Simple idle animation:
- scale Y to 1.05 and Z to 0.95
- scale Y to 0.95 and Z to 1.05
- repeat#unitytips #gamedev #indiedev #madewithunity pic.twitter.com/cW4o3mENRT

— Sergey Veraksich (@iveseni) 2017年1月3日

参考サイト様

https://qiita.com/hart_edsf/items/962ac03281b871dcc0df