I figured it might help others to see my recommendations so I'm going to post them here. If you have any concerns or questions please don't hesitate to shoot me a PM. I'm still working to fix-up or add some lore bits to the Atlas so it's understandable if you're confused or need help!

[@LordofthePies]

Okay so here are some of the notes I have for Light. I really enjoyed reading about the character. I always find tieflings to have some of the most interesting stories to tell. I really enjoyed the skillset you gave him. I think it could really create some interesting moments in the RP:
[hider=Light]
[b]Personality[/b]

Light would make an interesting addition to any party. It's definitely not an easy feat to RP a sadistic character. I am interested to see how he would react to some of the villains. I definitely allow for more villainous characters, but keep in mind that this world will react in kind to Light and this could make things difficult for you and your allies. 

The one thing that struck me as somewhat contradictory is that he is said to never break promises or deals because he finds it to be disrespectful. However you also note that he is a liar. I'm not sure if this is just when it comes to relaying information to others. Just keep in mind that he will be working for a guild in the RP. 

The way I was interpreting the above concern was that perhaps Light is a more politically-tact character. You did list diplomacy as one of his skills so maybe I'm not totally off. Perhaps he recognizes the importance of upholding promises with powerful people, but is also incredibly manipulative and lies when he has to. I could be off base with this, but I thought it was an interesting angle that would give the character some great in-game opportunities. I can go in-depth with Tiefling political structures should you be interested in exploring this. 

Also, something else to be careful with is how openly violent Light is. If he was raised in the Four Pillar Cities (Tiefling territory) in High Mist he'd have been sent to live his life as a Monk if he showed such ill-will for his kind and this is especially true considering he's a mage. 

[b]Backstory[/b]
Based on Light's backstory it sounds like he may have been raised in a human society. This will be elucidated further in the RP, but Tiefling culture is one of sacrifice and retribution. All tieflings are meant to take a generational group pilgrimage as teenagers to the monastic temples that dot the Wastelands of the southern-most parts of High Mist. This is especially true for mage tieflings who are sent as children.  So, if Light was raised in High Mist it'd be really important to hear about that in his backstory. What are his thoughts on the Dread God. Is it mere myth and fantasy to him? Another great mystery he wants the answers to?

If he was raised in human society I think his backstory makes a bit more sense as is. Typically Tieflings do become merchants or entertainers when fleeing/leaving High Mist. If he was raised in any of the non-Tiefling cities he'd be treated as an outcast (and potentially pursued given his status as a mage) were he to travel to The Pillar Cities without care of concealing his identity. 

[b]Abilities/Weaknesses[/b]
I think he's good in terms of his abilities! Destruction magic is fine by me. I have a few ideas that might influence how your character develops down the road. Of course this will be at your discretion. They'll just be ideas to think about when the time comes. 

However, one think I think needs a bit more work are Light's weaknesses and strengths. The personality flaws and positives are more fitting in the personality section. For weaknesses, mages are typically less able to handle close quarters combat and are fairly squishy. Light seems far more adept at mid-far range combat. I don't mind him having a rapier, but he is a young mage so I think his focus should be on one or the other for now with the potential to get more capable later on. 

For strengths it seems that Light is capable at keeping foes at a distance. 

Other things to consider:

Is Light quick on his feet?

Is Light more adept at reading incantations or fencing?

What types of magic might he be weak to? Spells involving water? Divine magics? Etc. (There aren't race-specific ones. I just mean spells that might cancel out your spells). 

These physical strengths and weaknesses will really help everyone out in combat situations. Allies can help make up for Light's downfalls, and enemies can exploit them. Keep in mind that Light seems to have a lot of potential outside of combat too. This isn't too say he's too strong now, but just remember to be wary of that kind of thing if you decide to change things around. As well keep in mind that he will grow in power throughout the RP. 
[/hider]