Me and my players got into an argument as to whether or not an Oni could take the Dodge action. This led me to question whether a monster can take normal actions other than the ones in its stat block. To me, at first, it seemed obvious that they could, but I am not a hundred percent sure.
Can monsters take actions that aren't detailed in their stat blocks?
The Actions section of the introduction of the Monster Manual (and the corresponding part of the basic rules) states:
When a monster takes its action, it can choose from the options in the Actions section of its stat block or use one of the actions available to all creatures, such as the Dash or Hide action, as described in the Player’s Handbook.
The actions available to all includes the Dodge action. See What are "the actions available to all creatures"? for more details, and Why do we assume that PHB rules apply to monsters? may be of use as well.
