10 Most Powerful Villains In Star Trek History
8. The Sphere-Builders
As beings who can phase through most attacks, and who can shoot energy beams from their hands seemingly just for fun, the Sphere-Builders were always going to be a bit of an intimidating threat to face. Combine this with the fact they managed to convince the Xindi's to work as their peons and help them build a weapon that would wipe out seven million people on Earth, and suddenly they're a very large threat indeed.
It's also worth mentioning that the weapon that does so is merely a prototype, meaning that the real version that was being built was no doubt capable of absolutely catastrophic destruction.
After this plan fell through, the villains would not be deterred, and would come narrowly close to wiping out humanity several times, only stopped literal seconds before they would have destroyed the Earth.
While the Sphere-Builders were exiled back to the trans-dimensional realm that they initially came from, it's worth remembering that they came unnervingly close to destroying humanity for good.