The subject of this article or section is part of Hallow's End, a seasonal event that lasts two weeks. Once the event has run its course, this will no longer be available until next year, but there are no guarantees.
There was an Easter Egg with Jesper, which involved the player summoning a Spring Rabbit. The pet would walk to Jesper and stand on the same spot, then Jesper would sit down for a moment and stand up. The rabbit disappeared. (This was removed in patch 3.3.3)