People love making Tieflings with all arrays of skin color. What do the rules say about that? And should you listen? Let's scope our some infernal bloodlines.
Flesh to Stone is a 6th level transmutation spell that has new mechanics from prior editions. Instead of instantly petrifying the target in ye olde "save or die" fashion, the target is restrained on the first failed save, and only petrified if they lose a “best of 5” save mechanic. Let’s examine how often its successful.
Contagion is a necromancy spell that requires an attack roll and a "best of 5" save mechanic to inflict a disease. Is this a good spell? Check your odds against the whole gamut of monsters.