Green Death (Franchise)

Dragons: Rise of Berk
The Green Death was stated to be a less aggressive cousin of the Red Death. It is likely a member of the same species, but has been given another name to differentiate it from the individual known as the Red Death, who couldn't be used in game as the dragon itself is dead. This may be a reference to the How to Train your Dragon books, in which the Green Death is a species of Seadragonus Giganticus Maximus.

School of Dragons
The Green Death also appears in School of Dragons, where it made its home in the old lair of the Red Death. However, a build up of magma and rock began to cause a release of toxic gas, or sulfur dioxide, around Dragon Island, as well as near the school. After clearing the problem, the Green Death got agitated with intruders in the island, but Toothless, who is now the Alpha, manages to calm it down. At that moment, Harald Forkbeard launches a harpoon into the Green Death, causing it to rampage so he could make his escape. Once the weapon is dislodged, the Green Death returns to the corona of the volcano.

The Green Death is not quite as aggressive as the Red Death. Instead of forcing other dragons to serve it, the Green Death lives alone, as well as searches for food itself. It scales are a shade of green, a reference to how it got is name. The games also depict it with some pink coloring on its horn and belly instead of tan like the Red Death.