Little Thornboldt always used to have trouble sleeping through the night, his fear of monsters and boogeymen waking him often with terrible nightmares. His beloved nursemaid found the solution, though, when she gave him a boogeyman of his own to scare away the others which might menace the child. 
“This little boogey loves you very much, Thorn, and he’ll scare away the other beasties and gobble up all your bad dreams and keep you safe until I come back in the morning.”

Spending a long rest cuddling with the Bedtime Boogey gives an creature advantage on Wisdom saving throws against nightmares.