(Or, a jelly that's not a fish, DVICE's own Evan Ackerman would contend.)
Even scarier than its looks, the Robojelly underwater robot is powered by hydrogen, which means it could conceivably never run out of energy because it can generate fuel from its natural surroundings. The robot was developed by roboticists at the University of Texas at Dallas and Virginia Tech for underwater search and rescue missions. Perhaps most disturbing is how its movements are almost indistinguishable from a real jellyfish.
You can see the never tired, undersea dwelling, singularity hive mind robot of your apocalyptic nightmares in action in the video below.