Kill your pet dog or cat (starve it, burn it, etc.). When the Grim Reaper arrives, plea and hopefully lose. If you win and the pet lives, kill it again. After losing, the Grim Reaper will turn it into a zombie. Your undead pet will still want to be fed, rested, and cleaned but will not die if you do not do those things. Note: You can still train and interact with your pet.