The threshold is the barier that the hero must cross in order to start their journey. It is the gap between the known and unkown world. The threshold has a threshold guardian. This guardian, usually the mentor, attempts to make them not cross the threshold. They may do try to stop them because they are not ready for the journey.
In Shrek, Donkey is the mentor to Shrek. He tries to deter Shrek from going to Duloc and confronting Lord Farquaad about all of the fairy tale creatures that have taken over his swamp. When they arrive in Duloc, Farquaad is holding a tournament to see who the best knight is to rescue Princess Fiona. When Shrek arrives, Farquaad changes the challenge to whichever knight can kill Shrek will go on the rescue mission. Shrek defeats all of the knights and makes a deal with Farquaad that if he brings back Fiona he will get his swamp back.
In Shrek, Donkey is the mentor to Shrek. He tries to deter Shrek from going to Duloc and confronting Lord Farquaad about all of the fairy tale creatures that have taken over his swamp. When they arrive in Duloc, Farquaad is holding a tournament to see who the best knight is to rescue Princess Fiona. When Shrek arrives, Farquaad changes the challenge to whichever knight can kill Shrek will go on the rescue mission. Shrek defeats all of the knights and makes a deal with Farquaad that if he brings back Fiona he will get his swamp back.