Politics
The Summer Court and the Gloaming Court are constantly
engaged in incomprehensible political maneuvering, and
many fey lords of both courts enjoy making adventurers act in
their interests. The relationship between the Summer Court
and the Gloaming Court is more akin to passionate rivalry
than actual animosity. However, that does not mean that
deaths do not occur, especially when it comes to their lesser
pawns.
Revenge
Fey have very long memories, and they see no qualm with
punishing a humanoid for a perceived slight done against
them from decades done ago or even for one committed by a
creature's ancestor. Fey revenge often is difficult to identify as
revenge, as it can often simply appear to be a string of bad
luck, a freak accident, or an unexplained disappearance.
Unseen Admirer
The fey find humanoids fascinating, and it is not unheard of
for a mortal to receive a secret fey admirer. This adoring fey
may provide their target mortal with secret assistance, such
as granting them advantage on Survival checks, bestowing
them with charms, or stymieing the efforts of the mortal's
enemies.
Of course, this has another side, too. Sometimes an
admirer becomes too obsessed and begins to feel entitled to
the target of their affection. Many heroes who found
themselves experiencing a streak of excellent luck suddenly
disappeared without a trace one day, spirited away by the fey.
Others may suddenly find themselves or their loved ones
plagued by bad luck from a jealous admirerer.
Liminal Places
These are the places that are only strange afterwards. They
are towns that only sometimes exist, mountains that can only
be seen during a storm, deserts that are bigger inside than
they are on the outside. A party may visit a town, sleeping in
the inn, buying supplies, and speaking to citizens, only to find
out when they reach the next town that the town they're
describing does not, in fact, exist.
Fey Magic
Fey are creatures of magic. They don't use spellbooks, they're
written of in spellbooks. Every fey has an innate connection
to the Weave, and as such they all possess the ability to shape
magic in significant ways. In much the same way that a
human might tie a knot, a fey might be able to bestow or
create a magical effect. For example, a powerful fey might be
able to cast geas on a creature even if that spell is not in their
Innate Spellcasting option, while others can grant charms or
even blessings. A fey can typically only do this one or two
times per day, and never while in combat.
A good rule of thumb is to gauge the strength of the magic
by the CR of the fey invoking the curse.