In Star Trek, there's always someone out there who is bigger, faster, stealthier, and has more firepower. Ulimately, some of these opponents were just misunderstood, and simply wanted to communicate. Some of these spacefaring vessels were only threats once they fell into the wrong hands. However, in the end, we're dealing with imminent danger that will tip the balance of power on a planetary scale or greater. What are the biggest threats out there on the final frontier?
http://m.ranker.com/list/the-most-devastating-spacefaring-threats-in-star-trek/switchdoctor,
Crystalline Entity
Star Trek: The Next Generation ("Datalore")
V'ger
Star Trek: The Motion Picture
Borg Cube
Star Trek: The Next Generation
USS Enterprise NCC-1701-E
Star Trek: First Contact
Space Amoeba
Star Trek: TOS "The Immunity Syndrome"
USS Defiant NX-74205
Star Trek: Deep Space Nine ("The Search")
Doomsday Machine
Star Trek: TOS "The Doomsday Machine"
Species 8472 Bioship
Star Trek: Voyager
Whale Probe
Star Trek IV: The Voyage Home
Jellyfish
Star Trek (2009)