A machine that fists. Such machine can insert itself into the vag or more commonly, the anus - which it will then continue to pound out your insides.
Fistatron is also well known for taking things out, crushing them, and destroying them.
(Not always used in a sexual manner).
Me: I am a Fistatron! I will pummel your insides till you are no more!
Yourmom: Please... Don't!