Element Empire Storyline
Etna feel in love with Gabriel Haywood when he saved her the first time. they had a thing going, but when Gabriel turned good, they broke up. After Etna tried to turn good for him, she learned that he had Amy and Emily with Rainbow . She now plots to separate him from Rainbow so she can have him and be his wife and lover. She formed the Shadow Force just for that reason and for back up. She is more powerful than the whole Shadow Force put together.
She joined the Cosmic Empire mainly because Gabriel and Rainbow did, which didn't exactly make the Skeleton King dance with joy.