Death Mage

Choose two spells from the Necromancy school, each of which must be no higher than level 2, and add them to your spellbook for free. In addition, whenever you gain access to a new level of spell slots in this class, you can add one spell from the Necromancy school to your spellbook for free. The chosen spell must be of a level for which you have spell slots. Necromancy spells do not need to be on the Wizard spell list for you to add them with this feature.

Once per turn, when you damage a creature with a Necromancy spell, you can choose one die result from the damage roll and gain that many Temporary Hit Points. If you choose a die that rolled its maximum value, and the spell is a leveled spell, you can receive any of that die's Temporary Hit Points as Hit Points. The number of damage dice you can apply this feature to increases to two, then three, then four at Wizard Levels 5, 11, and 17 respectively.

Undead creatures controlled by your Necromancy spells gain a +2 bonus to their attack rolls and add your Intelligence modifier to their saving throws. In addition, when you use your Life Siphon feature, you can redirect any Hit Points and Temporary Hit Points received to any of these creatures (no action required).

You can bolster your ability to sustain spells by sacrificing some of your vitality when you cast them. Each time you cast a spell that requires Concentration, you may chose to lose 5 Hit Points for each level of the spell or spell slot (whichever is higher) and reduce your Hit Point maximum by the same amount for the spell's duration. If the spell is a cantrip, you lose 5 Hit Points only. Until the spell ends, you do not make Concentration saving throws, your Concentration on the spell does not end due to you having the Incapacitated condition, and you have Disadvantage on Constitution saving throws.

When Undead creatures controlled by your Necromancy spells deal damage with a feature in their stat blocks, this counts as damage from your leveled Necromancy spells for the purposes of your Life Siphon feature.