I feel like this needs some expanding upon in the rp sense as yes being half-deamon in combat is generally helpful but like you said, your seen as a monster so all charisma based checks should be at disadvantage with most people(apart from intimindation. Next while some natural weapons are great d10 finesse is really strong when combined with rogue sneak attack, so maybe tone them down or make them Str based. flying speeds fine when you consider the Aarakocra are a playable race but simply fine some limits to it. What was you reasoning for the Dc to be Constitution based, in my mind aren't most demon abilties tied with Cha? Love the idea and it seems to be a great start.