School Of Entropy

Called the true domain of necromancy, the School of Entropy goes with many steps further down the forbidden path of harnessing the powers of life and death, dabbling in equal parts arcane and divine. These scholars study entropic forces obsessively, seeking to master negative energy thought to once been beyond their reach.

Entropy Savant

Beginning when you select this school at 2nd level, the gold and time you must spend to copy a necromancy spell, or a spell that deals necrotic damage, into your spell-book is halved.
Also all spells that deal necrotic damage or are from the necromancy school are considered to be on the wizard spell list for you, but other wizards can not copy these spell from your spell-book into their own spell-book.

Drain Life

at 2nd level, Your knowledge of life and death allows you to steal the life energy from creature touched by your dark spells. Once per turn when you reduce one or more creatures to 0 hit points with a spell of 1st level or higher, you gain temporary hit points equal to twice the level of the spell or 3 times the spell's level if the spell dealt necrotic damage or belongs to the school of necromancy. You don't gain this benefit for killing constructs.

Alternatively, when a creature you can see within 30 feet of you is reduced to 0 hp, you may use your reaction to reap it life energy, gaining temporary hit points as though you killed witha necromancy spell of 1st level.

Necrosis

Starting at 6th level, you've learned to suffuse your spells with negative energy, leaving your enemies weakened and vulnerable. Whenever you successfully hit one or more  creatures with a spell that deals necrotic damage, or one or more creatures fail a saving throw against a spell you cast from the necromancy school, you can choose a number of those creature up to half your wizard level rounded down to suffer one of the following effects until the end of your next turn: 

Festering Wounds. The creature suffers an additional 1d4 necrotic damage whenever it receives any piercing, slashing, or necrotic damage.

Withering Muscle. The creature's movement speeds are reduced by 10, and it subtracts 1d4 from all damage rolls is makes

Decaying Mind. The target has disadvantage on Constitution saving throws to maintain concentration, as well as Intelligence, Wisdom, and Charisma checks.

Rotting Flesh. The creature cannot regain hit points, and has disadvantage on Strength and Dexterity skill checks.

Constructs are immune to this feature. You can use this feature a number of time equal to yoour Intelligence modifier (minimum 1). You regain all expended uses on a long rest.

Death's Reach

At 10th level, you can briefly tap into the Negative Energy plane and imbue the weave around you with its energies. As a bonus action you enhance your spells, causing the range on any spell from the school of necromancy, or a spell that does necrotic damage, to be doubled. Spells with a range of touch gain a range of 30 feet. These benefits last until the end of your turn.

Additionally, necrotic damage you deal ignores resistances and treats immensities as resistance.

Necrolord

At 14th level, you've become a master of negative energy and entropy, and your body is sustained by it. You no longer need to eat, drink, sleep, or breathe, gain resistance to necrotic and poison damage, and immunity to necrotic damage of your own spells and abilities. When you cast a spell that deals necrotic damage, you can choose any number of targets you can see to be immune to the damage of your spell.

Additionally, when you affect creature with your Necrosis feature, you may have the suffer two effects instead of one.You still expend expend only one use of the Necrosis feature.

Finally When you use your Drain Life feature, you gain additional temporary hit points equal to your intelligence modifier