Ive had a lot of help lol. Kobold Press’ Midgard setting had a few new Derro monsters (Fetal Savant and Dogmoles) and Pathfinder’s Golarion setting has a lot of good Derro lore to work with. The most time consuming part is gonna be building all the Derro npc stats and balancing all the encounters. Pathfinder’s Derros are also the closest to what their actually based on, which was a fascinating rabbit hole. https://en.wikipedia.org/wiki/Richard_Sharpe_Shaver