Aurora and Mirage were Immortalis born from the combination of Air and Water power. These two elements combined gave them super fluidity which manifested itself in Aurora as the ability to walk through matter, and in Mirage as the ability to warp light around him (Invisibility).
*These guys were based on the Darkspore cover art. The blending of blue and orange tones on a dark backdrop inspired this. I also realize that Aurora (unintentionally) resembles Stringer.