Round its tower was kept a watch
by those with eyes so keen.
But its deep darkness was not such
as to keep elven lights unseen
Shadowmere
Note: due to glitches with FAS41, the Encounter report said the answer failed but the character received the arty anyway. (Scott Baltes)
Luvailin or Shadowmere was a mere in Eldamar under the shadow of Oiolossë.
Tolkien Gateway: Luvailin