Seven Kingdoms: Seowyn's Crossing
The Madjack is a green-skinned Slaad that invaded the Goblin land of Gristamere. It was imprisoned within the mining colony of Kor Malkosh, where ancient goblin wizards imprisoned it deep beneath the earth. Slowly, its location was forgotten, until miners working in the recent years accidentally freed it.
It used its powers to summon elementals and send them out to lay waste to the surrounding towns, as it began to grow in strength, preparing to strike out in conquest. Luckily, before it could, the Fire Wasps interfered and slew it. It still attempted to continue its plans by impregnating The Shaper with its chaos phage, but he was able to resist it with aid from Eustace.