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.
If anyone would be willing to do this I'd be most grateful. But if it sounds like too big a task, then I won't hold it against you. Thanks for putting up with my rambling.