Then Hazel heard a sound in the distance—like the whinnying of a horse. She must’ve been imagining it, but she cried out desperately, “Arion! Over here!”
A tan blur came ripping down the street and onto the pier. The stallion materialized right behind the gryphon, brought down his front hooves, and smashed the monster to dust.
Hazel had never been so happy in her life. “Good horse! Really good horse!”

The Son of Neptune, Chapter XLII