Animate the Dead
This subclass requires a hero to be truly evil and willing to defile the sanctity of life. This magic is evil, and while it is powerful, the consequences for it's use are immeasurable on one's soul.
Zombies made with this class in mind: https://nimble.monster/families/necromancer-s-familiars-5e2ccvk4vx8tat14y7dd1d8gwf
Level 3
Animate Dead.
You gain the following spell:
Animate Dead Tier 1, 5 Actions, Single Target
Reach: 1. Effect: Animate a single corpse, transforming it into an undead of Level 1 or lower according to how it died. If it does not meet the conditions for any specific undead, it becomes a Zombie or Skeleton. This undead obeys your commands until midnight, after which it will seek to violently destroy any and all life it finds.
You may command any number of undead you control in this way with actions during combat. These actions require the undead to hear you. 1 action may command them to move, 1 action may command them to attack, 1 action (as a reaction) may command them to interpose. Without your commands, the zombies follow you but do not fight.
Upcast: +1 level of undead or +1 corpse.
Level 7
Student of Necromancy.
You unlock Necromancy spells.
Level 11
Undead Leader.
Your Animated Dead's attacks are made with advantage of they are in Reach: 2 of you.
Level 15
Perfected Control.
(1/Safe Rest) You may pick one Animated Dead to be forever loyal by performing a ten minute ritual with it. It will not begin to disobey you at midnight. This effect ends when you perform this ritual again.