Might also be servuo compatible.
This is a script i unearthed from an old server i used to run.. spawn a zombiex and it will attack anything that isn't already dead. On death, the mobile becomes infected, and itself turns into a zombiex. This package contains baseundead, and zombie nest - a pile of bones that spawns zombiex's until it is destroyed, and an undead slayer deed which can add the undead slayer to any weapon (as a reward for killing zombies).
Note that the chance of receiving this as a reward is set to 99% for testing, simply check for 99 and change to whatever value you want. The script also has a "rot" delay, where zobies would eventually rot and die. i disabled this, just look in zombiex comments. also change might be required in distro edits if this is enabled.
Second note: WARNING! a single zombie can totally take over an entire continent if not kept in check. so i recommend spawning in a contained area