According to the Raising Mercury Facebook page...
Mercury was found at a little over 5 ounces, with his eyes still shut, missing both front legs and all but one toe on one of his back legs. We brought him in to bottle feed, and this is his journey.
The rescuers believe that Mercury lost his limbs after being hit by a week whacker. However, Mercury is still an active and adorable kitten who doesn't let anything get in his way.