Wizards who pursue the School of Witchcraft learn to infuse their spells with curses and dark magic. 

Witchcraft Savant

2nd level School of Witchcraft feature

The gold and time you must spend to copy a spell with the debuff tag into your spellbook is halved.

Cursecraft

2nd level School of Witchcraft feature

You can manipulate your magics to infuse them with dark magic. You gain a number of cursecraft points equal to twice your proficiancy bonus. When you cast a spell, you can expend your cursecraft points in the following ways. 

Impair Ability. When you cast a spell that targets a creature, you can spend a number of cursecraft points up to your spellcasting modifier to force the target to make a charisma saving throw against your spell save DC. On a failed save, the creature gains a reduction to all their ability checks equal to the number of points you expended for a minute. They that repeat the save at the end of each of their turns, ending the effect early on a success. 

Cursed Thralls. When you deal damage to a creature with a spell, you can spend a cursecraft points to change the damage type to necrotic. If this damage reduces the creature to 0 hit points, they must make a charisma saving throw against your spell save DC. On a failed save, the target regains 1 hit point and are charmed until the end of their next turn. While charmed in this way, they obey any verbal commands that you issue to them (no action required by you). You can specify a simple and general course of action, such as "Attack that creature," "Run over there," or "Fetch that object," but you cannot choose how it does so or which actions it takes. If the creature completes the order and doesn't receive further direction from you, it defends and preserves itself to the best of its ability.

You regain unspent cursecraft points when you finis a long rest. 

Master of Hexes

6th level School of Witchcraft feature

You can to fine tune your hexes with expertise. You add bestow curse to your spellbook if it was not there already. When you cast bestow curse, you can choose two options for the nature of the curse. In addition, you can expend a number of cursecraft points equal to the level at which the spell was cast to cast the spell without requiring concentration. 

Armor of Transformations

10th level School of Withcraft feature

You can transfigure your enemies to protect yourself from harm. When you are targeted by an attack from a creature you can see within 60 feet of yourself, you can use your reaction to cast the polymorph spell targeting the creature who attacked you. 

You can use this feature once, regaining use after a long rest. 

Total Control

14th level School of Witchcraft feature

You can take complete control of others with your magic. When you charm a creature with your Cursed Thralls feature, the duration is increased to 48 hours. While charmed ion this way, you can use your action to take total and precise control of the target. Until the end of your next turn, the creature takes only the actions you choose, and doesn't do anything that you don't allow it to do. During this time, you can also cause the creature to use a reaction, but this requires you to use your own reaction as well.

Each time the target takes damage, it makes a new Wisdom saving throw against your spell save DC. If the saving throw succeeds, the effect ends early and the creature is reduced to 0 hit points.