AnimationState.speed

Description

The playback speed of the animation. 1 is normal playback speed.

A negative playback speed will play the animation backwards.

Additional resources: AnimationState.time, AnimationState.wrapMode properties and WrapMode enum.

using UnityEngine;
using System.Collections;

public class ExampleScript : MonoBehaviour
{
    public Animation anim;

    void Start()
    {
        // Walk at normal speed
        anim["Walk"].speed = 1.0f;

        // Walk at double speed
        anim["Walk"].speed = 2.0f;
    }
}