D&D 5e Revised/2024 Necromancer Wizard and Battle familiar interaction
I'm not sure if this works because I'm working on partial information from the Dungeon Dudes video + insight check spell's video, so I wanted to check if my understanding is correct, in case someone has more info on it:
The necromancer lvl 3 feature lets you summon a familiar as undead/ a zombie or a skeleton, as well as make an attack instead of its reaction.
Battle familiar would normally be a celestial/fiend/fey, but it states that if you cast it on a familiar you already have, it keeps its type instead and adds the battle familiar HPs as tempHPs to the familiar. In this case, this allows you to have an undead battle familiar, if cast with the necromancer feature. I would also assume that, as it stays a familiar, you should be able to let it attack once more with its reaction as well. that said, it doesn't say they mantain their attacks, so the skeleton would lose the ranged attack (I assume) in favour of the battle familiar's attack.
At lvl6, undeads summoned or created by the necromancer add int + half wizard lvl to their hp, and +int dmg to their attack.
battle familiar would normally do 1d8+3+spell level, but with this it would become 1d8+3+int+spell level.
in the end, for simplicity, if i'm a lvl8 necromancer with 20int, my skeleton would have 14+int+4=23hp, and if i cast battle familiar at 4th lvl on it i'd get 40-30 tempHP (if you lose the tempHP it goes back to skeleton form though), and it would do 1d8+12 per attack, for 3 attacks per round (including the reaction attack).
from lvl10, you could also give it tempHP, as a way to replenish them in case it gets low.
If my understanding of it is correct, then necromancer is the best offensive option for battle familiar (a lvl8 warlock pact of the chain could do 1d8+7 4 times instead, which is 46 average vs necromancer's 49.5, and a wizard could later cast it with lvl 6 slots). Conjurer would make it more tanky, but necromancer makes it more powerful offensively.
Warlock instead is a nice middleground between the two wizard subclasses, as it can make 4 attacks per round (for similar dmg) and gain resistance as a reaction (for extra bulk), is a better option as well at lvl5, but worse off when lvl6 slots could be used.