Kiygas is what happened when Kylose fused with a being called "Giygas". It's gender is it since it's a mixture of a male and a female. It got down into the core of Earth to try to destroy the planet using an army of cyborg Irkens called "Sporgs". Before it could destroy Earth, Zim and Kai killed it by singing a set of meledies called "the gardians of life".
Kiygas has the same personality as Giygas.
Kiygas has red skin, no antenae, a black uniform, red tentacles, dark purple eyes, and it's PAK is red mist.