Unity 3D and the Puppet2D tool .

This tool can help you to animate sprites with Unity 3D.
You can create 2D skeletons, skin your characters to the bones, and create really easy to use controls that make animating 2D characters.
The tool come with this price $30.00 from this link.
First you need to create a 2D project into Unity 3D.
After you download this tool into your Unity 3D  then you can deal with this tool.
The main goal is to assemble sprites into a character and then create the desired animation.
Then the animation will be embedded in your project just like any animation.
See the next tutorial from official youtube channel of  Puppet2D tool: