Twilight is a campaign-specific power, but can certainly be applied elsewhere.
Note: it REALLY helps to watch 'Ninja Scroll' and the Elf vs. Dark Elf battles in 'Lodoss Wars' (both are works of anime) -- most of the abilities in Twilight got their first start in my head while I watched those shows, and I'll use examples from the shows below.
Twilight is not a power restricted to any one people or species, but in practice, the only people who have exhibited/explored the ability are the three known branches of the Eldar: the Noldor, Mori, and Vari.
TWILIGHT (35) [10] Initiate [5] Extended Locale [5] Inter-Shadow Twilight [5] Lead in Twilight [5] Speak in Twilight [5] Shadow Fade
Initiate
As an initiate of Twilight, an individual can literally enter a shadow (not a Shadow) and
basically teleport themselves to another shadow nearby. The maximum range of this
teleport is uncertain, but seems to roughly equate to the initiates psyche+10 in
yards/meters. (IE: Amber level psyche = 10 yards.) Usually this skill is used
by the average Mori or Noldor warrior in combat, either to seek escape or to attain a
tactical advantage. It is NOT possible to move to another Shadow with only this ability,
nor is it possible to take 'passengers' of any kind. (There are indications that while
the user is 'between' the shadows, they are actually in another place, which is called the
'Eternal City' -- some sort of mysterious, golden-washed wood tainted with a hint of the
Dangrous: look at the Forest of No Return in Lodoss Wars for a decent image of it.)
From beginning to end, the teleport takes about 5 to 10 seconds, depending on range.
Initiation is achieved through training, as with Sorcery, rather than assaying some Power Source, as with Pattern.
The use of this ability is tiring to anyone of less than Amber endurance. (The eldar average endurance is quite high as a race.)
Extended Locale
Extended Locale moves the maximum range of the shadow-port out to psyche*10 in
yards/meters. Nothing else changes regarding time of the 'port, or restrictions. (Look at
Ninja Scroll for a good example of this Power.) The use of this ability is VERY tiring to
anyone of less than Amber endurance.
Inter-Shadow Twilight
Basically the same as Extended Locale, but allows the user to reach out to a shadow in a
neighboring Shadow. Note that only neighboring Shadows are reachable in a single
jump, and as such the fastest use of this power is only just a BIT faster than a
Shadowwalk of a Pattern initiate.
The use of this ability is very nearly IMPOSSIBLE to anyone of less than Amber endurance, though it is not terribly taxing to those above Amber level.
Lead in Twilight
By drawing the energies of the Eternal City through to This Side, a master (or mistress) of
Twilight can surround his or her following in Twilight, moving them all from Shadow to
Shadow without 'Jumping'. Speed is about equivalent to the Royal Way of Pattern
Initiates, and the APPEARANCE of this power differentiates from user to user: Witnesses
will see followers of Brigid slowly being swallowed by gloom, while those watching Artanis
lead her people will see her followers move away from them in the hazy, golden light of a
perfectly restful Twilight. The Vari do not use this power.
The use of this ability is impossible to anyone of less than Amber endurance.
Speak in Twilight
Allows the user to contact any other Twilight Initiate -- note that any twilight initiate
to contact THEM -- the contact can only be initiated by the possessor of this ability, not
the other way around. Range is inter-shadow and can be quite far (perhaps even from Arden
out to Ygg), depending on relative psyches (Artanis is said to be a match even for Fiona),
and other circumstances.
Shadow Fade
This is power that the possessor (in practice, only the more skill leaders of the various
Eldar factions) can turn on an off. When 'on', the user's body literally fades out of
existence when it intersects with shadows, and fades back in when they reenter the
light. This makes them very hard to hit with ranged weapons, especially in wooded
regions, and also makes them very difficult to track. The power is somewhat hard to
visualize, and can BEST be seen in the scenes in Lodoss Wars when Deedlit is chasing or is
chased by dark elves -- they frequently fade from vision while jumping from branch to
branch in the trees.
Maintaining this power 'on' requires an endurance higher than Amber level at a minimum.
Note: each separate power MUST be taught to a user by someone who already has the ability, and the three most advanced powers (Speak, Lead, and Fade) are closely guarded skills.