Horned Serpents are snakes with horns on their heads.
The Senior Year Adventures[]
The Chalice of the Gods[]
In order to clean Iris's staff in the River Elisson, Percy Jackson, Annabeth Chase, and Grover Underwood have to distract the serpents. At first, Grover plays his panpipes as they chase, but as he tires Percy takes his place. He lured the serpents to a rock and becomes surrounded. However, he thinks of Annabeth and the staff teleports him to his friends.
| The Senior Year Adventures | |
| Books: | The Chalice of the Gods | Wrath of the Triple Goddess |
| Main Characters: | Percy Jackson | Annabeth Chase | Grover Underwood |
| Secondary Characters: | Sally Jackson | Paul Blofis | Eudora | Hecuba | Gale | Nope |
| Minor Characters: | Naomi | Barbara | Elevator Security Guard | Blanche | Lucius | Margaret | Sparky | Li'l Killer | Mrs. Foray | Dr. Samuels | Dr. Sharma | Peter Stuyvesant | Mrs. O'Leary | Chiron | Connor Stoll | Clovis | Harley | Valentina Diaz | Juniper |
| Gods: | Ganymede | Iris | Hebe | Elisson | Poseidon | Zeus | Demeter | Hera | Hermes | Athena | Geras |
| Titans: | Rhea | Kronos | Hecate |
| Mythical Creatures: | Nereid | Nymph | Horned Serpent | Hellhound |
| Related Content: | Rick Riordan | Percy Jackson and the Olympians | The Heroes of Olympus | The Trials of Apollo | The Nico di Angelo Adventures |