Bone for Blood

Choose one living Medium or Small humanoid within range. Humanoid is cut with a dagger, their eyes are replaced with onyxes and magical glyphs are carved into their skull during the exhausting dark ritual. Humanoid must be within range during the whole duration of the ritual.

When the ritual is over, onyxes explode into black dust, the sacrifice dies, its flesh rapidly decays and humanoid becomes a Key-Bound  Skeleton. (The GM has game statistics for these creatures.) The key used in the ritual takes a bony structure and becomes a binding key - vessel containing shards of the soul of the humanoid.

Optionally, you can additionally use a dead body of another humanoid of the same race as the sacrifice. In that case, the living humanoid is used only as a component for the spell and the long-dead soul is bound instead.

As a bonus action on each of your turns, you can mentally command any creature you animated with this spell if the creature is within 120 feet of you (if you control multiple creatures, you can command any or all of them at the same time, issuing the same command to each one) or in range. You decide what action the creature will take and where it will move during its next turn, or you can issue a general command, such as to guard a particular chamber or corridor. If you issue no commands, the creature only defends itself against hostile creatures. Once given an order, the creature continues to follow it until its task is complete.

As an action, you can command one or more creatures created with this spell within 120 feet to pull the rest of their soul from the bodies into their binding keys. While in soul-less state, skeletons fall into the inanimate state and unrecognizable from a pile of bones. As an action, you can revert the process and pour souls back into bodies, returning them to the usual state.

The soul trapped inside a key is bound to you and is under your control until it (soul) is destroyed, until you lose your soul, until you exceed the limit of binds, or until the key is destroyed, after which soul is released any creature animated by the key reverts to the inanimate state.

After the key is created, you can re-use it to perform the ritual with humanoid of the same race as one trapped into the key. In this case, ritual casting time is reduced to 8 hours (additionally reduced by 1 hour for every 3 levels of wizard of the School of Necromancy). In this case, soul trapped into the key is linked to a new body, draining soul of the new sacrifice and expelling it into the afterlife. This process empowers the trapped soul, giving associated skeleton additional bonuses(the DM will have the specifics) up to 5 times after which the soul becomes too strong and escapes, melting the key. Key durability could be extended by using more expensive materials (+1 additional usage per 100gp cost of the key).

You can be bound to the number of keys equal to your wizard level divided by 4 (wizards of the School of Necromancy are limited to the 1 bound key per wizard level).

Key must be made or rare component, the price for the key is 100gp * (number of already bound keys + 1).