I posted this idea a while ago, see what you think of it:
As a fan of dark magic in general, Necromancy is one of my favorite
aspects of the dark arts. I would love nothing more then to command my
undead minion horde against my enemies, collect the remains and merge
them into my horde of abominations, or summon skeleton legions when I
need them. For Minecraft 1.12 and beyond however, there really isn't any
options for this aside from the 'Overlord mod and 'Electroblob's
Wizardry' which while a good option by themselves aren't good enough for
really role-playing as an unholy magic wielder.
There was a Necromancy mod by AtomicStryker but it hasn't been
touched since 1.7.10, I also saw someone talk about creating a Lich mod
with the focus being learning about Necromancy until you could make the
transformation into an undead Lich yourself.
For me, the perfect Necromancy mod would allow you to build your
minions out of pieces, equip them with weapons, armor and even magic of
your choosing, level them up as they battle for you and even upgrade
them as you continue your research into the dark arts. There would be
skill and tech trees, magic spells to aid you and your minions and an
assortment of monsters you could command.
What do you think? Too big for what you were thinking of?