Fresh Holly

Fresh Holly can be used while riding a mount and will transform your mount into a reindeer until you dismount. Flying mounts can still fly, and will lift off with a jingly bell sound, leaving an energy / snowflake trail. Fresh holly requires Feast of Winter Veil, meaning it will only work during the event.

Source
Obtained during the Feast of Winter Veil seasonal event by kissing the special holiday NPC found in Inns standing under some mistletoe.