I am working on a character. The concept is a Gnome who's warlock mother traded her to the fiend patron, for extra power (the mom was a really bad warlock, and this extra power made her mediocre, which is ten times stronger than before). The Gnome was corrupted into a Tiefling-ish form, and forced to battle in the gladiator pits for the fiend's entertainment. My question is, how would I go about this race? Is there a precedent Gnome/Fiend race? Or should I just have a Tiefling with a small size class?