Actually the problem has nothing to do with NPCs performing the action or the action being a custom action. This will give the same problem.
Code:
"Test"
Every turn: try cutting.
The Testing Room is A Room.
Afterward wrote:
Code:
Creeping is an action applying to one thing.
Every turn:
Try Margot creeping.
What's going on here is that you have defined an action to apply to one thing, then *not* supplied that thing, therefore the noun is still nothing and the error message is given.
There are three ways you can fix this.
1. You can add a rule for supplying a missing noun to automatically set the noun, like so.
Code:
"Test"
Creeping is an action applying to one thing.
Rule for supplying a missing noun while creeping: now the noun is the person asked.
Every turn: try creeping.
The Testing Room is A Room.
2. You can supply the noun directly, like so.
Code:
"Test"
Creeping is an action applying to one thing.
Every turn: try creeping the player.
The Testing Room is A Room.
3. You can redefine the action to apply to nothing, like so.
Code:
"Test"
Creeping is an action applying to nothing.
Every turn: try creeping.
The Testing Room is A Room.
Overall, you need to make sure you have the right number of nouns to fit the action.
Hope this helps.