How about some love for Tiefling Warlocks out there? This ability replaces Dark One’s Own Luck
Power In the Blood
You’ve give yourself over to your fiendish ancestry. You don’t use charisma for spellcasting or Charisma based skills and saves, but instead use Constitution for all spell casting depending effects, skills, and saves. All spells you cast using your Infernal Legacy trait now use Constitution for their effects as well. In addition, you gain one additional use of all spells gained from your Infernal Legacy trait.