What monsters, cryptids and mythological creatures from human culture would be the most dangerous if unleashed in a major city?

Don’t pick anything that’s overpowered or unbeatable. Make it interesting. An example would be a Minotaur.

The Boneless.

Oh, I dunno, the Boneless WERE unleashed in a major city and they only killed a few people...

Because they were still figuring things out and there weren't a great many of them. I have no doubt that a full on Boneless invasion would have caused a great deal of damage and terror. They even had a way to neutralize a TARDIS.

Humans.

Most dangerous overall would be a biological (pathogen caused) "fast zombie" with extreme aggression and high transmission rates. By the time the authorities figure out it isn't just some sort of new drug overdose reaction the only practical containment protocol requires isolating the infected area and killing anything that tries to exit. Since, with the possible exception of the DPRK, there isn't a country on Earth that would have both the willingness AND the blind obedience of its troops to pull that off (The Red Army while Stalin was alive might be another candidate, but even then all it takes is one small sector to fail to shoot Littles on sight to lose the perimeter. Get the R/O of measles (12-18) and a four or five day infectious before frank symptom expression and you get a wild fire. High speed spread, destroys everything in its path until it hits a barrier it can't breach and burns itself out in short order (I'm not a big fan of the zombies live for years, or even months, school too many mouths to feed and limited food supply, including other zombies).

Next level is a Kaiju with a bad attitude. This can be stopped, but it takes a truly cold blooded SOB to do it. Hit the thing with a set of ToT nukes. Despite Godzilla, the reality is that for about 20 meters diameter sphere around a 100kT detonation nothing made of matter can exist. The heat and pressure equal the interior of star and not only breaks molecular bonds between atoms, but strips off the electrons of the individual atoms. It takes the term "vaporised" to a whole new level. Of course it will also kill a substantial percentage of the population within 6 miles of the detonation, explaining the need for a REALLY cold-blooded bastard to have the launch codes.

If monsters from outside the Whoniverse are permitted, then I'd have to nominate the Replicators from Stargate SG1. The originals, before the writers ruined them by giving them human appearances.

First off:

To Judibug: First off, you have just described Star Treks Borg.

Secondly: the most recent Godzilla remake clearly shows him surviving 2 massive nuclear explosions at close range.

In fact one of them healed him of serious injuries and the other gave him time to catch his breath when he was knocked down.

the most recent Godzilla remake clearly shows him surviving 2 massive nuclear explosions at close range.

In fact one of them healed him of serious injuries and the other gave him time to catch his breath when he was knocked down.

To think people have the cheek to criticise DOCTOR WHO just cos Hand of Fear implied you could survive a nuclear explosion by ducking down behind a car with your fingers in your ears...

Hey, I'm not saying that I believe it- all that I'm saying is that it happened in the movie.

Pip and Jane Baker would be dangerous if they were unleased in a major city.

Pip and Jane Baker would be dangerous if they were unleashed in a major city.

Indeed they would, as both are now dead.

That would make them either zombies or vampires.

There might be a good story there somewhere!

Yeah, some may see it as disrespectful but once you've turned THE BRIG into a Cyberman...

I know she's long gone now, but I suspect it would be dangerous to unleash Mary Whitehouse on a city.