Honestly i think tieflings to be a bit under powered. The penalty to cha is fine by me but darkness was nerfed and that destroys part of the fun. I have a tiefling wizard whose father is one of the horseman and honestly if darkness wasn't nerfed his signature would be to drop it before any fight started, especially against a powerful caster destroying their line of sight. but unfortunately i cant. the fiendish sorccery i find pointless because the extra spells would be better. some of the good pieces of tiefling gear, mainly the halo of inner calm provides spell Resistance which will becomes useless as it is only 13. the sacred bonus to saves is nice. the outsider dammaging spells, well there is a lot of them more than personal spells and honestly there are not enough sucubi and incubi to make it fair. so yes tieflings are definately underpowered, not by much but they are