Undead Evil

Undead Evil zombies:
- Use custom sounds and attack animations
- Use a multi-stage alertness system to allow stealth gameplay
- Spread out and zig-zag on the move (no single-file lines)
- Claw their way out of the ground on spawn
- Throw things at you, especially when they can't reach you (watch out for flying bricks)
- Are knocked down by melee attacks
- Have a chance to become crawlers when knocked down
- Have a chance to trip over bodies, over each other, when turning too sharply, and when whiffing an attack
- Attack and damage vehicles
- Ignore high-flying helicopters
- Have un-stuck protection: zombies that can't move (spawned inside of a rock or something) will eventually die