Lichdom

in order to become a lich you must first tread the path of a necromancer therefore the begining levels of this class are the same as necromancer wizard but the later levels you transform into a lich which is way cooler

Necromancy Savant

Beginning when you select this school at 2nd level, the gold and time you must spend to copy a necromancy spell into your spellbook is halved.

Grim Harvest

At 2nd level, you gain the ability to reap life energy from creatures you kill with your spells. Once per turn when you kill one or more creatures with a spell of 1st level or higher, you regain hit points equal to twice the spell’s level, or three times its level if the spell belongs to the School of Necromancy. You don’t gain this benefit for killing constructs or undead.

Liches undead

At 6th level, you add the animate dead spell to your spellbook if it is not there already. When you cast animate dead, you can target one additional corpse or pile of bones, creating another zombie or skeleton, as appropriate.

Whenever you create an undead using a necromancy spell, it has additional benefits:

• The creature’s hit point maximum is increased by an amount equal to your level.
• The creature adds your proficiency bonus to its weapon damage rolls.

At this point your transformation into a lich has begun giving you resistance to Necrotic damage

Undead transformation continues

at 10th level as you get deeper into the study of necromancy you transform more and more gaining resistance to cold damage and and your hit point maximum can’t be reduced.

final transformation

Starting at 14th level, create an area with a 100ft radius centered on a point of your choice that your undead do not need to have control reasserted over them if any undead leave this area the timer will begin and will not pause upon reentering the domain, you can only have one Undead domain area active at a time and it takes 1 hour to set up the domain, the domain lasts until a new one is formed or you dismiss it with an action, you do not need to be in the domain for this feature to stay active. in addition gain immunity to Necrotic damage and Vulnerability to Raiant damage

Also you can use magic to bring undead under your control, even those created by other wizards. As an action, you can choose one undead that you can see within 60 feet of you. That creature must make a Charisma saving throw against your wizard spell save DC. If it succeeds, you can’t use this feature on it again. If it fails, it becomes friendly to you and obeys your commands until you use this feature again.

Intelligent undead are harder to control in this way. If the target has an Intelligence of 8 or higher, it has advantage on the saving throw. If it fails the saving throw and has an Intelligence of 12 or higher, it can repeat the saving throw at the end of every hour until it succeeds and breaks free.