Crossing Alien hybrid (hybrid, predominately mahachai) with plakat (splenden) would create fatter/shorter bodied hybrids/aliens. Color would depend on the genetics/color of the plakat (because most if not all aliens are metallic,full mask/partial mask,spread iridescence).
As for crossing other species, results may vary, for example
Crossing male Splenden (black dragon) with Imbellis female (wild type brown) yielded 100% females with wild type brown body and red fins.
Imbellis/Splenden hybrid female (wild type brown, red fins) crossed with male splenden (Turqoise, spread iridiscence) yielded some fry with imbellis-like color patterns (red crescent, see picture below)as well as some fry that resembled normal multicolor/redwash splendens. Behaviour wise, they are very shy and will seldom flare in the presence of humans.