Monsters under bed
Monsters may appear underneath beds in The Sims 3: Supernatural and The Sims 4. However, only children can see and interact with them.
In The Sims 4, monster repellant can be purchased to ward off monsters; Sims may also attempt to befriend the monster.
In The Sims 4 you can buy the monster repellent to keep the monster away, or even try to make a relationship with them.