Phaia

When necromancer kills a creature that is neither a construct nor undead with a spell of 1st level or higher, Phaia regains hit points equal to twice the spell's level, or three times if it is a necromancy spell.

Phaia is a 12th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 15, +7 to hit with spell attacks). The necromancer has the following wizard spells prepared:

Cantrips (at will): chill touch, dancing lights, mage hand, mending

Level 1 (4 slots): false life*, mage armor, ray of sickness*

Level 2 (3 slots): blindness/deafness*, ray of enfeeblement*, web

Level 3 (3 slots): animate dead*, bestow curse*, vampiric touch*

Level 4 (3 slots): blight*, dimension door, stoneskin

Level 5 (2 slots): Bigby's hand, cloudkill

Level 6 (1 slots): circle of death*

*Necromancy spell of 1st level or higher

Melee Spell Attack: +7 to hit, reach 5 ft., one creature. Hit: 5 (2d4) necrotic damage.