Composite Skills are skills that are created using two or more skills in unison. Unlike skills that are created by fusing or evolving, where the component skills are erased, Composite Skills are manifested by simply 'linking' two or more skills together while still retaining the original skills. An example of this would be Hell Flame that is used by utilizing Fire Manipulation, Area Boundary and Black Lightning.
Composite can be both active or passive skills, depending on the skills themselves, and are generally akin to Extra Skills. Moreover, they are also low performance compared to, if say, the individual had the skill as an independent skill. An example would be an individual linking different kind of resistances and defensive skills to emulate Multiple Barrier, compared to one having the Extra Skill Multiple Barrier itself. Since certain Composite Skills simply 'emulate' actual Skills, they are naturally lower performance. However, that may not be the case for original Composite Skills.