These rules were found on List of Challenges (Legacy and Other) for Sims 4 – Page 17 — The Sims Forums

Your Sims now have the ability to kill and attack others, defend themselves from other sims and more! Arm yourself with a chainsaw, a knife, a gun or even your bare fists. This mod packs a punch literally and physically. There are so many options and so much to explore to this mod. You have the ability to join gangs, or become a serial killer. The Sims 4 Statistics For Xmiramira. At this time, Xmiramira has 8,745,247 views for The Sims 4 spread across 443 videos. There's over 20 days worth of watchable video for The Sims 4 published on his channel, or 82.08% of the total watchable video on Xmiramira's YouTube channel.

Sims 4 Serial Killer Rules

GOAL: Basically to kill as many sims as you can within 3 weeks!
RULES
-You CAN’T ask sims to move in so that you can control them.
-You CAN’T use any mods that would initiate certain deaths.
-You CAN’T go to another world, make friends with someone and then invite them over, you must bring them inside from your street.
SETTING UP
-Lifespan must be on LONG
-You need to create your sim. Must be young adult and must have the evil trait. The other two can be anything you want.
-Can place your sim on any lot you want. Just note you will need space for you to live and rooms to lure sims.
-Money cheats are only allowed at the beginning when creating your house.
GAMEPLAY
Wait outside your house until someone walks past. Stop them and talk to them. Then when the ‘Go here together’ option is available, take them to their room and then leave and delete the door. You could kill them by letting them starve or drowning them. You must keep their graves in your garden and banish their souls to the Netherworld. Count how many sims you have killed at the end of 3 weeks. You can either count their graves or count how many ghosts are in your relationships panel.
REMEMBER: Don’t leave the lot while you have people in your house because when you come back, they disappear.
ADDITIONAL OBJECTIVE
Try to make children with as many of your victims as you can. If you run out of space in your family, kill a child. But their scoring still counts. Note that looking after babies will result in less time to trap victims because you must make sure they live; Unless you kill them to make space for more when you get up to 8 family members (Then its ok if they don’t live, you will need to kill them to make space.) You CAN’T make more than 1 baby with each victim.
SCORING
+50 for every sim that dies,
+30 for deaths by Cowplant,
+60 for becoming best friends with the Grim Reaper,
+90 for every child you make with your victim.
PENALTIES
-100 for using any cheats during the challenge.
-100 for breaking any rules.
-90 for any baby that dies without being killed.