#Monsters

###Class and class features are part of statistics too (including feats)

###Legendary Creatures have Legendary Actions as part of their statistics

#NPCs

When you give an NPC game statistics, you have three main options: giving the NPC only the few statistics it needs, give the NPC a monster stat block, or give the NPC a class and levels. The latter two options require a bit of explanation.

###Using a Monster Stat Block

The Monster Manual contains statistics for many generic NPCs that you can customize as you see fit, and chapter 9 of these rules offers guidelines on adjusting their statistics and creating a new stat block.

###Using Classes and Levels

You can create an NPC just as you would a player character, using the rules in the Player’s Handbook. You can even use a character sheet to keep track of the NPC’s vital information.

 

Class Options. In addition to the class options in the Player’s Handbook, two additional class options are available for evil player characters and NPCs: the Death domain for clerics and the oathbreaker for paladins. Both options are detailed at the end of this chapter.

Equipment. Most NPCs don’t need an exhaustive list of equipment. An enemy meant to be faced in combat requires weapons and armor, plus any treasure the NPC carries (including magic items that might be used against the adventurers).

Challenge Rating. An NPC built for combat needs a challenge rating. Use the rules in chapter 9 to determine the NPC’s challenge rating, just as you would for a monster you designed.

#PCs

Monsters

Class and class features are part of statistics too (including feats)

Legendary Creatures have Legendary Actions as part of their statistics

NPCs

When you give an NPC game statistics, you have three main options: giving the NPC only the few statistics it needs, give the NPC a monster stat block, or give the NPC a class and levels. The latter two options require a bit of explanation.

Using a Monster Stat Block

The Monster Manual contains statistics for many generic NPCs that you can customize as you see fit, and chapter 9 of these rules offers guidelines on adjusting their statistics and creating a new stat block.

Using Classes and Levels

You can create an NPC just as you would a player character, using the rules in the Player’s Handbook. You can even use a character sheet to keep track of the NPC’s vital information.

Class Options. In addition to the class options in the Player’s Handbook, two additional class options are available for evil player characters and NPCs: the Death domain for clerics and the oathbreaker for paladins. Both options are detailed at the end of this chapter.

Equipment. Most NPCs don’t need an exhaustive list of equipment. An enemy meant to be faced in combat requires weapons and armor, plus any treasure the NPC carries (including magic items that might be used against the adventurers).

Challenge Rating. An NPC built for combat needs a challenge rating. Use the rules in chapter 9 to determine the NPC’s challenge rating, just as you would for a monster you designed.

PCs

###Class and class features are part of statistics too

Since class levels and class features are also added to a monster's stat block, and the terms "statistics" and "stat block" are defined to be interchangeable (per the first quote in this answer), monster class levels and all the features thereof count as part of a monster's statistics.

###Class and class features are part of statistics too (including feats)

Since class levels and class features are also added to a monster's stat block, and the terms "statistics" and "stat block" are defined to be interchangeable (per the first quote in this answer), monster class levels and all the features thereof count as part of a monster's statistics.

Feats appear to be generally given by a class:

At certain levels, your class gives you the Ability Score Improvement feature. Using the optional feats rule, you can forgo taking that feature to take a feat of your choice instead.

Thus, as a class feature, Feats are also considered to be part of a monster's statistics.

###Legendary Creatures have Legendary Actions as part of their statistics

When a creature is a legendary creature it sometimes has special actions called Legendary Actions inserted into their stat block. These (as with everything else in the stat block) are considered part of the creature's statistics.

Note that some legendary creatures also have lair actions and regional effects. However, these appear outside the stat block and the Monster Manual makes it clear that not every legendary creature with those listed even has access to them. So these would not be considered as part of that monster's statistics.

###Class and class features are part of statistics too

Since class levels and class features are also added to a monster's stat block, and the terms "statistics" and "stat block" are defined to be interchangeable (per the first quote in this answer), monster class levels and all the features thereof count as part of a monster's statistics.

Basically, anything on the standard PC character sheet that is on the list above is considered to be a statistic.

###Class and class features are part of statistics too

Since class levels and class features are also added to a monster's stat block, and the terms "statistics" and "stat block" are defined to be interchangeable (per the first quote in this answer), monster class levels and all the features thereof count as part of a monster's statistics.

###Legendary Creatures have Legendary Actions as part of their statistics

When a creature is a legendary creature it sometimes has special actions called Legendary Actions inserted into their stat block. These (as with everything else in the stat block) are considered part of the creature's statistics.

Note that some legendary creatures also have lair actions and regional effects. However, these appear outside the stat block and the Monster Manual makes it clear that not every legendary creature with those listed even has access to them. So these would not be considered as part of that monster's statistics.

Basically, anything on the standard PC character sheet is considered to be a statistic.