Dopplio + Instantly is a match made in heaven.

This article is in progress, but here is the code snippet you need to setup a variable thumbnail in your Instantly campaign (make sure to change the variable names to exactly match your own):

<div>
    <a href="https://videos.dopplio.com/videos/{{Video ID}}/">
        <img style="max-width:300px;" src="https://cdn.dopplio.com/thumbnails/{{Video ID}}.gif">
    </a>
</div>