Obsidian Steed

A figurine of wondrous power is a statuette of a beast small enough to fit in a pocket. If you use an action to speak the command word and throw the figurine to a point on the ground within 60 feet of you, the figurine becomes a living creature. If the space where the creature would appear is occupied by other creatures or objects, or if there isn’t enough space for the creature, the figurine doesn’t become a creature.

This polished obsidian horse can become a nightmare for up to 24 hours. The nightmare fights only to defend itself. Once it has been used, it can't be used again until 5 days have passed.