Unify grab/bite attack.
The current addition in #23955 to cause bites to fail if there is no grab causes zombie bite attacks to still trigger, but not succeed. this nerfs zombies unnecessarily.
Zombies should attempt to grab if there is no grab on the target, bite if the current zombie has a grab, and otherwise randomly bite or grab with a chance based on the number of grabs on the target (more grabs mean greater chance of biting).
Zombies may have a counterattack where they impale themselves on an attackers weapon when stabbed, causing additional damage, but resulting in the attacker's weapon being stuck.
Once stuck, especially on a reach weapon, zombies may attempt to lunge further, causing still more damage but allowing them to reach the player or lodge themselves more firmly on the target's weapon.
As with ordinary weapon sticking, the player should be able to either move away from the target to attempt to un-stick the weapon, move toward the target to attack, or drop the weapon to remove the stuck state, leaving the weapon embedded in the target.
In order to make large groups of zombies threatening, but keep lone zombies manageable, we would like for zombie abilities to scale with number of zombies.
The grab/bite mechanics reduce zombie effectiveness when zombies are alone, but at some point characters become able to manage as many zombies as can physically fit adjacent to them (8), and difficulty scaling comes to a stop.
We can extend the threat from large groups of zombies by extending the grab concept further. Once a target is grabbed some number of times (i.e. 4), zombies would be able to trigger a new special attack "Rending" where all participating zombies pull on the target in all directions and cause damage.
In game terms, the zombies would add together their strength to deal armor-ignoring damage.
The player should be able to resist this attack by exerting their strength, but this would rapidly decrease stamina, so is ultimately futile.
Players in power armor or similar should be mostly immune to this attack.
Reach attacks, even from the most basic spears, trivialize kiting. The issue is that ordinary kiting carries a risk of a mis-step that can lead to the kited monster getting an attack in. Spears provide a buffer that allows these mis-steps to be recovered, leading to perfect kiting that isn't available from any other melee weapon type.
This is exacerbated by zombie attacks (bites) being potentially deadly.
One possible nerf is to add a "sticking modifier" to primitive spears to introduce a risk of a weapon stuck result from an attack, which limits mobility and makes attackers somewhat vulnerable to counterattack.
The stuck state would prevent movement, attempting to move would instead attempt to un-stick the weapon. Dropping the weapon would remove the stuck state, but of course relinquish the weapon.
A particular tactic that is overly easy to set up and too effective is setting up a chokepoint in a house window, resulting in this setup
As a result, the zombie in the window frame would be stuck after spending moves to enter the window, and the remaining zombies would be stuck behind that zombie. The player can then deal with just one zombie at a time.
A simple solution to this unintended behaviour is to have the "frustrated" zombies trigger a push action on the zombie stuck in the window. This would move the window zombie into the square with the player (triggering an opposed check to resist it) or diagonally into a square adjacent to the player. The pushed zombie should be "downed" to reflect tumbling through the window, but otherwise would be able to act normally (including executing a grab attack on the adjacent player). Meanwhile a new zombie would be free to enter the window tile and threaten the player or even have the pushing process repeated.