Defiled Mind

Young wizards who, in seek for knowledge or power reached to distant planes of existence, where their minds couldn't withstand the horrors of such places as Nine Hells or Pandemonium. Their brains are damaged, their souls are broken. Their bodies suffer from various, almost random anomalies from invisible eyes or melting flesh to sudden teleporting, but gain some exceptional powers like eternal youth and prophetic visions about past, present or even possible future.

Some say that wizard of defiled mind can be easily recognized as food he looks at rots, the corpses of his enemies fall apart and disappear in the blink of an eye. According to Master Domitius'es "Atlas of Curses and Anomalies", those touched by that curse tend to be Tieflings as they're more likely to have connection with horror domain. 

Those defiled unfortunates try their best to control their abilities or fall into chaotic personalities. Some orders of Mystra even run poorhouses for the most damaged, but history does not know any case of someone pured of that curse.

Neverending Suffer

Starting at 2nd level you stop aging in normal for your race way. Your hair don't grow anymore, your nails stay at that exact lenght you had before reaching second level and so on. For mechanical purposes you still benefit from resting altough your body gradually gets covered with more and more scars as wounds don't heal that easily anymore.

Your horror infused blood is white hot and deals fire damage equal to 1 per liter, to everyone not at least resistant to fire. Your breath starts stinking of sulphur and death, small animals are scared by your presence and others can definetely tell that there is something wrong with you.

If a creature can see your entire face, smell your breath or is good aligned and within 5ft. from you, you get disadvantage to all Persuasion checks against that creature.

Curse of Rotten Mind

Starting at 2nd level, whenever you fail any Intelligence based test, you instantly suffer 1d4 psychic damage.

Nightmares from Hell

Beginning at 2nd level whenever you try to sleep you have to roll Wisdom saving throw with DC 13. Failure means nightmares from your time spent in evil planes haunt your mind and you wake up with 1, additional level of Exhaust.

Chronological Anomaly

Beginning at 2nd level, you notice that time around you flows differently than anywhere else. You gain Initiative bonus equal to your Intelligence modifier.

Chaotic Implosion

Starting at 2nd level, whenever someone dies as effect of your spell, his body inplodes as his head or some similar part of body or structure is replaced by small black hole that disappears right after victims death. The replaced part or organ magically appears in your free hand or falls on the ground right in front of you.

Extreme Surge

Starting at 6th level, whenever someone rolls 1 on saving throw against any of your spells that deal damage, he suffers additional damage as if you would roll 20 on a hit.

Warped Prophecy

At 6th level you gain special ability that lets you once per Long Rest gaze into structure of time's fabric and experience a vision. You concentrate on any creature or object you can touch (including yourself).

Roll 1d6:
1-2:     the vision refers to target's past
3:        the vision is about target's current thoughts
4-5:    the vision refers to target's possible future
6:       you lost control on your ability, choose: you or the target suffers 2d12 force damage and is knocked prone

Involuntary Sacrifice

Starting at 10th level, once per Short Rest, whenever you take any damage you're not resistant to, you can choose to channel all of it to one of your allies. If that ally dies in effect, you also suffer that damage.

Chaotic resistance

Starting at 10th level, whenever you benefit from healing spell roll 1d6:

1-3: nothing changes

4-5: you're healed as usual, although your flesh, skin, brain and all tissues except skeleton meltdown and dissapear! They teleported somewhere in the multiverse and will be back after your next Long Rest. That changes nothing in your stats, but might be a disturbing view for others.

6: Instead of healing, the spell infuses damage on a caster. All the points you'd normally regain, hit your healer as a force damage. It that kills him, you suffer exact amount and type of damage instantly.

Blessing of the Watchmaker

Starting at 14th level, whenever any effect kills you in one way or another, you may choose to sacrifice all your remaining spellslots and be teleported to the last location where you've taken Long Rest without taking any damage. Your equipment and clothes are not teleported and drop on the ground in place you stood. If you have active Familiar, it also teleports as it's in fact another soul bonded with yours.

Mortal Bribery

Starting at 14th level whenever you cast a ranged attack spell that deals damage, you can increase that damage by up to 4 dice although the additional dice deal also damage to one of your allies in your eyesight.