Molly <broadcasting worldwide via hacked communication satellites>: "Greeting, Earthlings, I am Molly, Queen of the Planet of Sanctuary. On behalf of my people, I welcome you to the greater multiverse."
Might be easier and more palatable to play it all off as aliens and extradimensional invaders rather than supernatural and mythological shit creeping out of the shadows they've been tucked away in for centuries or millennium.
Rhampires? Parasitic aliens from Planet X. They've come for your blood!
Whampires? Spiritual parasites from Planet Y. They've come for your women! Or men! Possibly both!
Blampires? We don't know where the fuck they came from, but they wear Human corpses as meatsuits and are bad news so everyone should keep killing them.
Faeries? Cousins from the "5th dimension". Long history of interaction with Earth, hence the extensive, if heavily garbled and inaccurate "Faerie" tales, and intermingled bloodlines. Possible angle for a new business; DNA testing for Fey gene markers?
Five Fold Court of Fate? Benevolent explorers here to uplift their fellow sentients with the secrets of the universe, medicines to cure what ails you and fantastical technology seemingly plucked from science fiction. We come in peace!
And so on.
The reason for the sudden rise of invaders and visitors? Might as well blame the Americans, and everyone else who detonated nuclear weapons in the past 60 years. They "thinned the walls between dimensions" and made "<insert Star Trek-style techno babble> noise" which attracted them. What was once a relative handful of criminals and raiders, explorers and refugees who wandered to Earth throughout history is now a flood, and they cannot be hidden or ignored any longer. Think of the children!
It's all BS, of course, and plenty of people would know that from the outset or disbelieve for one reason or another, but the vast, overwhelming majority? They would eat this crap up and ask for more. A century of media in every possible format has been prepping modern civilization for contact with extraterrestrial life, for good or ill, whereas centuries of concerted effort have been invested in convincing everyone that the supernatural is merely superstitious nonsense.
The lie doesn't need to last forever, or even a decade, but just a few years would be enough to reach a new normal.