This is a datapack I've created in place of my creation of similar design using command blocks.
This datapack is an updated, advanced version that changes how the spider webbing cooldown works and how the zombie Fear slowing ability works (changed to use /attribute instead of /effect)

Zombies give a Fear score to players if within 10 blocks. The more zombies are nearby, the faster that score goes up. At 100 and 200, the player becomes slower, at 400 the player gains blindness and at 600, wither. Fear caps out at 700 and will go down once there are no zombies nearby.

Spiders will web the player if within three blocks (pretty much melee range for a spider). The cooldown is three seconds and the time until the next Web decreases only while the player is near a spider.

Creepers will stick to the player if they get within three blocks. You are required to either kill it very quickly or use a bow. There is no escape.

Skeletons will, once they have agro, continue to shoot at you until you are more than 100 blocks away or one of you dies.