It is a similie as you are comparing (something) to how sly the fox is. A similie uses the words "like or "as".
simile
The phrase "sly as a fox" is a simile because it directly compares Max to a fox using "as." If it were a metaphor, it would say, "Max is a fox."
He had fooled them all as he was as cunning as a fox. They knew he was as cunning as a fox, so they would need a very good plan to win.
Like a happy fox
Since there is no "like" or "as" in the sentence, it is a metaphor.
It is a similie as you are comparing (something) to how sly the fox is. A similie uses the words "like or "as".
It is not a simile!
simile for stuck
Smart as a Fox or Monkey ???
That is a good simile, yes.
Fled from the King like a rabbit escaping a fox.