This ones a little rare.
To my belief, Ebony only spawns during the night, on any of Moon states, I personally only found Ebony on “Waning” and “Full Moon” nights. The cat can also be found during key story events, where everyone is present for it. When you check your map, it’ll show you the time and day, as well as the state of the moon.
Note: Unlike the “Pet Charlie” achievement, this one actually has an achievement tracker, so it’s much better to keep track of it. Just like with Charlie, you can also “Pet” or “Praise” to progress the counter + grab 25 Arcane Knowledge each time.
I only know of several spawns as of present, but I will update the guide further as I find more:
— At the entrance to Ghost Rider’s Shop location, on the right side.
— In the Whispering Wood, at the side towards where the cliff side is with the altar, Ebony will be on the right side of it. (You also find an elemental rod there for a separate quest early in game).
— In Hunter’s Folly, on one of the pillar by the crypt door (I was not able to interact with it for some reason on my playthrough, the interaction button doesn’t always show at funny angles).
— At “Standing Stones”, by the first standing stone symbol and the center platform.
— In the library within the Abbey, at the very end by the fireplace.
— In the room past the hero barracks within the Abbey, where the Chapel is.
— In the common room during a story event; Magik’s birthday party, Ebony will be laying in the floor by the TV.