Vidrir was the leader of the Order of Seasons and once wielded Summer’s Edge in a great war against the Shadowfell
Vidrir is Odin in disguise
Elven control over magic is due to their proximity to a large rift between the mundane world and the elemental planes (Feywild and Shadowfell are closest)
A powerful magical barrier holds the elemental energies at bay (Forbiddence) and allows the elves to tap into the planes with some level of control.
The original Matriarch organized the ritual that created the barrier and lent much of her power to its formation.
No one has been born with the Matriarch’s gift for barriers in two generations, and the barrier is beginning to weaken.
A powerful entity from the Shadowfell seeks to take advantage of the weakening barrier to enter our world.