Magic Hybrids are the result of a liaison between either a Human and Demon or Human and Angel resulting in a child that is part human and part Demon/Angel. Such a person will be inherently powerful in either Dark Magic or Light Magic (Depending on the immortal parent) but never both.
More often the child is the product of human/demon parents since a human/angel partnership is extremely rare. This means that the child is usually a means in which a Demon can establish a presence in the Mortal Realm without breaking the agreement with the Angels.
However whilst that might be the intended reason for “creating” such a child often the outcome may not go as planned for in some cases the child has eliminated their demonic parent to seize power for his or herself or has chosen to rebel and use their Dark Magic to fight against evil rather than for it.