In an interview with the ABC TV Blog, the showrunner compared future episodes of the BBC drama to a "ghost train".
"Last year we reassured you [but] this year to hell with that - we're going to worry the hell out of you," he said. "[The monsters are] scary. Very scary.
"There's the Silence in [episodes] one and two, the Siren in episode three, the Gangers in five and six, [and] all these are more than just freaky costumes and masks. There are scary ideas here."
Moffat, who previously described opening episode 'The Impossible Astronaut' as "a belter", also revealed that the next seven episodes will have a stronger overall arc.
"Oh, there's a big story being told this year, and major mysteries from the very off," he confirmed. "We're barely ten minutes into episode one before our heroes face a dilemma that they'll be staring at months from now. And there will be no easy answers."
The new series of Doctor Who begins on April 23 on BBC One in the UK and BBC America in the US.
Watch the new full-length Doctor Who trailer below:
> New Doctor Who trailer scene-by-scene