Ah, yes, Ariel. There are two things I think of when I watch this episode: hands of blue, and the Ariel Ambulance.
If you've dipped feet into the world of the Browncoat, you'll know that the hands of blue villians are underused. They are scary, methodical, and have the coolest and goriest brain melting weapons - ever. These villians appear in two episodes and are scary as hell. They are very terminator like and feature blue gloves which, by itself, isn't all that scary but just watching them work makes my skin crawl. Unfortunately, we don't see them at all after this episode (unless you've read the comics) and we learn what happens to them afterwards.