at 10th level, wizards of the arcane tradition of necromancy have become so exposed to undeath itself that they gain resistance to necrotic damage and their hit point maximum can never be reduced by any means. hang on to this information, it will be important in a second

create homunculus is an spell from xanatars guide to everything that does exactly what it sounds like, it creates an homunclulus, but here is the interesting part:

"whenever you finish a long rest, you can spend up to half your hit dice if the homunculus is on the same plane of existence as you. When you do so, roll each dice and add your constitution modifier to it. Your hit point maximum is reduced by the total, and your homunculus's hit point maximum and current hit points are both increased by it [...] The reduction cant be removed by any means before [you finish your next long rest], exept by the homunculus's death"

now, this is an rather interesting spell that has some fun risk/reward stuff built into the mechanics, but here is the big thing: the hit point gain of your homunculus is not necessarily the same as the hit point maximum loss to you, read carefully, you roll your hit dice, and that number seems to be used for both the hit point gain of the homunculus and the player, meaning that if your wizard happens to be an necromancer and high enough level to add create homunculus to his spellbook, he can theoretically (depending on your DM's interpretation of the spell and how much the table focuses or rules as written vs rules as intended) increase the hit point maximum of his homunculus without really lowering his own hit points. This is hardly an game-breaking exploit, just an very interesting one.

now, create homunculus is actiually an really interesting spell for more than that reason, for instance, unlike find familliar, there is nothing in the rules that forces the homunculus to always follow your commands, the spell only states that the homunculus is "your faithful companion",  meaning that it is possible (though improbable) that the homunculus might betray or leave you if it has enough reason to do so.

And speaking of find familliar, since this is an spell with an range of touch, you can technically cast it via your familiar, with potentially interesting results. Speaking on this matter, the find familliar spell states the following:
"finally, when you cast a spell that has an range of touch, your familiar can deliver the spell as if it had cast the spell" Now this wording makes it unclear if the familliar is for the purposes of the spell the caster of the spell, but assuming it does (there is probably an official ruling by crawford himself but i dont do research) in that case you could theoretically (assuming your familliar can survive 2d4 piercing damage, most dont) create one homunculus for yourself and one homunculus for your familliar (casting the spell and then allowing your familliar to use their reaction to deliver the spell, cutting themselves with an dagger and alowing its blood to fall on the components, the spell must be cast for your familliar before it is cast on you, otherwise it will fail), and then cast similaricum and let your similaricum cast create homunculus once themselves and once with their own familliar, and suddenly you have four homunculi directly or indirectly under your controll 

note: with the wording "as if it had cast the spell" RAI probably meant "at the familliars space" sort of like the new alchemical homunculus stat block infusion from the new artificer class.

the spell is probably much more easy to cast with your familliar if you use true polymorph on it to give it an form with hands and thus one who could easily stab themselves with an dagger, but you should be able to do without

the familliar must be close to you during the entire casting and close to the material component, the 1000 gp jewel encrusted knife used as the spellcasting focus does not have to be the spell the caster uses to cut themselves, important when you use this spell as an find familiar