Meatlug

Meatlug is the unnamed Gronckle from the film that was kept for Dragon Training.

At the film's climax, Hiccup taught his classmates how to ride the dragons before they flew off to rescue their tribe from the Red Death/ The gronckle was ridden by Fishlegs.

In Gift of the Night Fury, it is revealed Fishlegs named his Gronckle Meatlug, and Berk is preparing to celebrate Snoggletog for the first time with their dragons when suddenly the dragons all leave.

Fishlegs is revealed to have chained up Meatlug from leaving until Hiccup accidentally releases the Gronckle and it flies off with him. Inside the barn where Fishlegs kept Meatlug, he, Astrid, Snotlout, Ruffnut and Tuffnut discover that Meatlug is a she when they find her eggs in the hay.

Meanwhile Meatlug, with Hiccup on her back, flies to an island filled with dragons and hteir newly-hatched babies where Hiccup realizes the dragons came here to lay their eggs. Hiccup manages to return all the dragons and their babies to Berk where Meatlug immediately goes to feed her hatchlings which she left at the barn and is tackled by a happy Fishlegs. Meatlug presumably partakes in Snoggletog with her rider as Fishlegs is holding two of her babies.