Xanos

 Relentless Endurance (1/Day). When Xanos is reduced to 0 hit points but not killed outright, he can drop to 1 hit point instead.

Savage Attacks. When Xanos scores a critical hit with a melee weapon attack, he can roll one of the weapon's damage dice one additional time and add it to the extra damage of the critical hit.

Eyes of the Dark. Xanos can cast the darkness spell by spending 2 sorcery points or by expending a spell slot. If he casts it with sorcery points, he can see through the darkness created by the spell.

Font of Magic (7 Sorcery Points/Day). As a bonus action, Xanos can use sorcery points to create spell slots and vice versa. He can convert spell slots to sorcery points at a rate of 1 spell point per spell slot level. He can convert sorcery points to spell slots at the following rate: level 1 for 2 sorcery points, level 2 for 3 sorcery points, level 3 for 5 sorcery points and level 4 for 6 sorcery points.

Metamagic. Xanos knows the metamagic options below. He can use only one metamagic option on a spell unless otherwise written.
 Careful Spell. When he casts a spell that forces other creatures to make a saving throw, he can protect some of those creatures from the spell's full force. To do so, he spends 1 sorcery point and chooses up to three creatures. A chosen creature automatically succeeds on its saving throw against the spell.
 Subtle Spell. When he casts a spell, he can spend 1 sorcery point to cast it without any somatic or verbal components.

Hound of Ill Omen. As a bonus action, Xanos targets a creature he can see and summons a hound within 120 feet of it, spending 3 sorcery points. The hound has all the stats of a dire wolf, with the following changes:
1) The hound is size Medium, not Large, and it counts as a monstrosity, not a beast.
2) It appears with 3 temporary hit points
3) It can move through other creatures and objects as if they were difficult terrain. The hound takes 5 force damage if it ends its turn inside an object. 
4) At the start of its turn, the hound automatically knows its target's location. If the target was hidden, it is no longer hidden from the hound. 
The hound appears in an unoccupied space of your choice within 30 feet of the target and rolls initiative. On its turn, it can move only toward its target by the most direct route, and it can use its action to only attack the target. The hound can make opportunity attacks but only against its target. Additionally, while the hound within is within 5 feet of the target, the target has disadvantage on saving throws against any spell you cast. The hound disappears if it is reduced to 0 hit points, if its target is reduced to 0 hit points, or after 5 minutes.

Strength of the Grave (See Text). When damage reduces Xanos to 0 hit points, that isn't radiant damage or a critical hit, he can make a Constitution saving throw with a DC of 5 + the damage taken to drop to 1 hit point instead. After the saving throw succeeds, Xanos can't use this feature again until he finishes a long rest.

Spellcasting. Xanos is a 7th-level spellcaster. Charisma is his spellcasting ability (+6 to hit with spell attacks, spell save DC 14). It knows the following sorcerer spells:
Cantrips: fire bolt, mage hand, message, minor illusion, thunderclap
1st Level (4 slots): chromatic orb, mage armor, shield
2nd Level (3 slots): darkness, mirror image, suggestion
3rd Level (3 slots): fear, fireball
4th Level (1 slot): dimension door

Light Crossbow. Ranged Weapon Attack: +3 to hit, range 80/320 ft., one target. Hit: 5 (1d8+1) piercing damage.

Dagger. Melee or Ranged Weapon Attack: +6 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 5 (1d4+3) piercing damage.

Fire Bolt. Ranged Spell Attack: +6 to hit, range 120 ft., one target. Hit: 11 (2d10) fire damage.