TL;DR: The controller's purpose is to guide the rest of the horde to you and aid them in combat. It does not engage in direct combat, but instead finds a high location where it can focus on the player and guide the rest of the horde to you.
Mechanics:
Spawns at a high location, capable of climbing walls but not leaping like the spiders. Once it spots it's target, it locks on to them. When this happens, the player should get some highly visible UI effect (such as an overlay of the zombie's face or similar) so that they know they've been found and targeted by a controller.
Targeted player receives an exponentially stacking debuff that increases the damage they take. Starting off at 25% increased damage and doubling every 10 seconds. After 10 seconds it'll be 50%, after 20 seconds it'll be 100%, after 30 seconds 200%, etc... The goal here is mostly to make sure that even for tanky characters this isn't a party boon. It may be beneficial during a blood moon to let a tankier character keep the debuff for a little while... but after just 1 minute, they'll be taking 16x damage.
The controller forces retargeting of AIs to their target. If there aren't nearby zombies for them to control, they will summon more similar to screamers and force them to target their target. So the horde is going to go after that player. Cops will spit at them. Vultures will go after them, etc...
Finally, the player's vision is constantly being drawn towards the controller. This is both positive and negative. Certainly nobody wants their aim being messed with, but it also makes it fairly easy to find the controller. Just move your aim to follow where it's already being drawn and you are guaranteed to eventually be aiming directly at the controller's head. Useful during a blood moon when night visibility can make it hard to find the loan zombie who isn't moving.
More advanced variants could do things like pull your vision towards it, but never actually on to it, pull your vision towards it, but push your vision away from actually being able to aim directly at it, push your vision away from it entirely, cause increased hunger or thirst when it targets you, or other effects.
Mechanics:
Spawns at a high location, capable of climbing walls but not leaping like the spiders. Once it spots it's target, it locks on to them. When this happens, the player should get some highly visible UI effect (such as an overlay of the zombie's face or similar) so that they know they've been found and targeted by a controller.
Targeted player receives an exponentially stacking debuff that increases the damage they take. Starting off at 25% increased damage and doubling every 10 seconds. After 10 seconds it'll be 50%, after 20 seconds it'll be 100%, after 30 seconds 200%, etc... The goal here is mostly to make sure that even for tanky characters this isn't a party boon. It may be beneficial during a blood moon to let a tankier character keep the debuff for a little while... but after just 1 minute, they'll be taking 16x damage.
The controller forces retargeting of AIs to their target. If there aren't nearby zombies for them to control, they will summon more similar to screamers and force them to target their target. So the horde is going to go after that player. Cops will spit at them. Vultures will go after them, etc...
Finally, the player's vision is constantly being drawn towards the controller. This is both positive and negative. Certainly nobody wants their aim being messed with, but it also makes it fairly easy to find the controller. Just move your aim to follow where it's already being drawn and you are guaranteed to eventually be aiming directly at the controller's head. Useful during a blood moon when night visibility can make it hard to find the loan zombie who isn't moving.
More advanced variants could do things like pull your vision towards it, but never actually on to it, pull your vision towards it, but push your vision away from actually being able to aim directly at it, push your vision away from it entirely, cause increased hunger or thirst when it targets you, or other effects.
