Hello! There is a few ideas my brain suddenly had :
-Zombies follow each others. If a zombie hear a zombie, he will try to follow it to check what he heard.
-Longer days/nights : Best for Survival I think.
-more you hold left click with a bat for example, more it hurts.
-Sometimes, the knife get stuck in the zombie’s head. Then you’ve to hold left click/right click to remove it.
-Zombies have fast, sudden and vague moves when they saw you, However they’re calm when there isn’t any human alive.
-Darker nights when there’s fog/clouds.
-Bring zombies with a vehicle.
-Personalise animations of our character (4 choices for example).