|ST:TAS#20A Practical Joker|
Escaping a Romulan vessel the Enterprise heads into a cloud.
There, strange things happen. Machines play tricks on the crew. They escape and return to make the Romulans follow them. When the Romulan ship is in the cloud the Enterprise quickly leaves and now it is the Romulans who are prey to the cloud-like life form playing tricks on them.