The onyx mastiff statuette is a magical item that Vox Machina obtained in the Feywild. The fey creature Artagan, posing as a satyr named Garmelie, tried to steal it from Vex'ahlia. The dog was summoned in "Cloak and Dagger".
The command phrase of "good doggy" is etched in Elvish on the bottom of the statuette. If the bearer uses an action to speak the command phrase and throws the figurine to a point on the ground within sixty feet, then it becomes a living mastiff for up to six hours. The mastiff has an Intelligence of eight, can speak Common, and can see invisible creatures and objects. It has a bite attack and can make sight and hearing checks. At the end of six hours, or if the creature drops to zero hit points, or if someone uses an action to speak the command phrase again while touching the creature, then it reverts to its figurine form. Upon reverting to a figurine, the statuette cannot be activated again for seven days.