Dragon Catching Day
|“|| Wartihog and Dogsbreath got into a loudly whispered fight over a Gronckle, a heavily-armored brute with fangs like kitchen knives sticking out in such numbers that it couldn't keep its mouth shut. Dogsbreath won, then managed to drop it as he was trying to bundle it into his basket. The weaponry of the beast made a horribly loud catter as it landed on the floor of the cavern.|
The Gronckle opened its evil, crocodile eyes.
|— Book 1|
Seaslug was not awoken however, and stayed in hibernation.
Dealing with the Green Death
Later, though not specifically mentioned, Seaslug is a participant in the Final Initiation Test on Thor'sday Thursday. He partakes of the uncontrollable all-out dragon brawl that breaks out during the test, causing all the Hooligan and Meathead initiates to be exiled for being unable to control their dragons.
After the arrival of the Green Death on Berk, the Hunting Dragons all hide away and decide what to do - Obey or Desert. The dragons are only loyal to their masters when it suits them and "are not the sort of creatures to back a loser." Seaslug, along with the other hunting dragons, decide to go along with their masters to see who won - the Green Death or the humans. Seaslug and the other hunting dragons toss feather bombs at the Green Death and Purple Death, while hurling insults at the colossal dragons - all part of Hiccup's plan. Ultimately the two huge dragons kill each other.
|“||My master will tear this Hiccup limb from limb and throw him to the gulls.||”|
It appears that each Hunting dragon accompanies his or her master during educational lessons, such as the 'Board-an-Enemy-Ship' lesson in the Pirate Training Lesson. Though Seaslug does not figure into the story of How to Speak Dragonese, he does appear in an image aboard Dogsbreath's and Snotlout's boat, the Sparrowhawk, ramming into the boat of Hiccup and Fishlegs.
Seaslug finds himself pulled along by Dogsbreath to a 'Herding-Reindeer-on-Dragonback' Lesson on Huge Hill on an extremely hot day. He and Dogsbreath are to learn to herd reindeer while Dogsbreath rides a Riding Dragon for the first time.
Like most Gronckles, it is heavily armored and has fangs like kitchen knives.
|“||That's not a dragon," jeered Seaslug, Dogsbreath's dragon, who was an ugly great Gronckle with a pug nose and a mean temper, "that's a newt with wings.||”|
|— Book 1|
Seaslug is described as mean, and is a bully of Toothless much as Dogsbreath is of Hiccup.
|"How to Train Your Dragon":||Appears||"How to Ride a Dragon's Storm":||Absent|
|"How to Be a Pirate":||Appears||"How to Break a Dragon's Heart":||Absent|
|"How to Speak Dragonese":||Pictured||"How to Steal a Dragon's Sword":||Absent|
|"How to Cheat a Dragon's Curse":||Absent||"How to Seize a Dragon's Jewel":||Absent|
|"How to Twist a Dragon's Tale":||Background||"How to Betray a Dragon's Hero":||Absent|
|"A Hero's Guide to Deadly Dragons":||Absent||"How to Fight a Dragon's Fury":||Absent|