For each creature in the Monster Manual, a few special cases are listed for skill checks if applicable. For every other skill check, how do you determine whether the monster has proficiency? (proficiency bonuses listed by CR in MM p.8)
e.g. There are no skills listed for the Balor. Does that mean the Balor is not proficient at any skill? Is the proficiency bonus added to all monster skill checks? GM's choice?
Best Answer
The Monster Manual explains the Skills entry in a monster's statblock on page 8. The section begins with the following sentence:
So if a monster is proficient in a skill, that is reflected in its Skills entry. If a skill isn't listed in the Skills entry, the monster isn't proficient with it.
Like everyone else, monsters can use their ability modifier without proficiency for skills they aren't proficient in. This works out better for monsters then it does for most people, though, because they don't have to deal with point buy - to use your Balor example, it doesn't have an ability modifier less than +2. This would be impossible for a player character using point buy, and incredibly unlikely for a player character rolling their ability scores.