Nikora's Triple Stryke is a female dragon that appears in the expansion pack "Rise of Stormheart" of the game School of Dragons.
Somehow this dragon and her unhatched egg was captured by Nikora Stormheart. Stormheart gassed her with aerosolized Grimora venom on multiple occasions and sent her rampaging through Dragon's Edge. At one point, Dagur the Deranged arrives on Dragon's Edge, and helps chase her away. Unfortunately, a 'gift' Stormheart sends to Hiccup contains the Triple Stryke's egg.
Ultimately, the game player, Fishlegs, Heather, and others are able to devise a way to inject salt water into the dragon's system and free her from the Grimora venom.
This Triple Stryke has the same color patterns as Sleuther, with a golden yellow belly and a maroon red top.