Gish, otherwise known as a fighter/wizard, is one of my favorite character types. In 5th Edition, this can be very effectively built using any number of techniques, including–but not limited to–the Eldritch Knight, fighter/wizard or fighter/sorcerer, Pact of the Blade warlock, and various other esoteric class and spell combinations. However, the original gish comes from githyanki lore: a powerful warrior and wizard, capable of blade and spell attacks.
So when the player characters came upon a githyanki silver sword that literally fell from the sky, I knew that having them face githyanki without having a gish in their midst would be a terrible disservice. Having her ride in on an armored nightmare with a flameskull familiar was probably a helpful image as well.
But… what do I know…?