When you use the Unearthly Swiftness to play first location
and second location with an encounter, the 5th and 6th locations of your Trail are droped off.
If both of encounters at the 5th and 6th locations are "New vampire", whether bothof them will mature or only first one?

From memory, when you mature a New Vampire, your trail drops to 3 cards. If this is correct, the 2nd new vampire is "lost" as it is part of the trail that dropped off.

Your trail is wiped to one card, IIRC. And yes, the second new vampire is lost (not matured) because you resolve them one at a time. The second location never even reaches the end of the trail, let alone get matured. The rule about wiping your trail was most likely put there specifically to prevent Dracula from dropping too many new vampires at once.

I think that with "Unearthly Swiftness" things would work differently than what answered:

What the card does is to give Dracula an extra movement right after the normal; so the Dracula's turn will be something like this:

(Timekeeping Phase)

Movement Phase

Movement Phase

Action Phase

So Dracula will move and place a Location card on his trail making the sixth card to drop off (and the first vampire to be set aside for mature purposes - except if Dracula wants to store the location in the catacombs).

Then Dracula will move again and place another Location card on his trail making another card to drop off (also the second vampire is set apart for mature purpose - always unless the location is going to go to the catacombs).

Then the Action Phase begins and (unless there's one (or more) hunter in the second location) Dracula must place an encounter ONLY on the second card.

Finally Dracula can decide to mature the encounters he set apart before: both, only one or none (and I don't see why he shouldn't decide for both, it's 4 points on his track!). According to his choice he then scores the points, clear the trail to 1 card, etc.

Then (if it has not won) his turn is over.

This is how I think it would work...

Byga, you scored a very good point here. I cross-checked the rules, and there is nothing saying that you cannot mature two encounters in the same turn.

But there is this clarification in the FAQ that maybe can change a little the things:

Maturing Encounters
Whenever an encounter drops off Dracula’s Trail, the Dracula player may mature the encounter – even if Dracula is at sea, and even if Dracula is forced to move because of a card such as Stormy Seas.

So, the key word here is "whenever", which means that it's not related to Dracula's Action Phase. Thus, Unearthly swiftness makes two cards to be moved, and according to this FAQ entry, it seems to me that you can activate the first or the second, but not both (at this point a very good move could be activate the second one, while the first one goes straigth into the catacombs, ready for a Seduction card on some of the Hunters. This should allow even maturing encounters even on other occasions (Evansion comes to my mind, but even fleeing combat as a Bat, and similar things), increasing a little the chance of Dracula to win (which, in my opinion, is good)

Besides, this would fix a +4 point to the final score, which basically means game over