What are two incidents in the story "The Canterville Ghost" that illustrate Oscar Wilde's tendency to reverse situations into their opposites?

Wilde most aptly and humorously portrays these reversals by depicting the poor Canterville ghost's dilemma in his encounters with the Otis family. The ghost, obviously supremely confident of his ability to scare the wits out of whomever he encounters, sets about doing the same to the American family who were the new owners of Canterville Chase, his favorite and only haunt.

The first incident occurs when, on the third night of the family's stay, the ghost decided to give them the fright of their lives, as he had done to others so many times before. At one o'clock, the ghost walked down the corridor outside Mr. Otis's bedroom, loudly clanking his chains. He expected that the man would be terrified. However, in a surprising and humorous twist, Mr. Otis takes a small oblong phial out of his dressing-case and looks down the passage. He sees what should have been a frightening vision, as described by Wilde:

"Right in front of him he saw, in the wan moonlight, an old man of terrible aspect. His eyes were as red burning coals; long grey hair fell over his shoulders in matted coils; his garments, which were of antique cut, were soiled and ragged, and from his wrists and ankles hung heavy manacles and rusty gyves."

Mr. Otis is completely unperturbed and nonchalantly advises the ghost to have its rusty chains oiled since they are making too much noise. He procures a phial of lubricant, "Tammany Rising Sun Lubricator," for this purpose. He informs the ghost that the oil is very effective and that he will provide more if the ghost needs replenishment. He then places the bottle of oil on a marble table, closes his door, and goes back to sleep.

The ghost is indignant and smashes the phial on the floor. His plan backfired completely.

A second occasion occurs on a Sunday night when the ghost once again tries to shock the family. He attempts to walk around in his old armor but instead hurts himself when he falls. When Mr. Otis and his two sons reach the hall, they find the ghost in agony and rubbing his knees. The two boys shoot pellets at him with their pea-shooters whilst Mr. Otis points a gun at him, commanding that he hold up his hands. The ghost is enraged and with a wild shriek sweeps out of the room. He then decides to laugh his most horrible laugh at the top of the staircase. This tactic also fails miserably, for Mrs. Otis appears in the door and offers him a lotion, "Doctor Dobell's tincture," to cure his supposedly sore throat.

The ghost is enraged and wants to turn himself into a large black dog but gives up doing so when he hears footsteps coming up the stairs. Just as the twins come up to him, he turns phosphorescent and disappears. 

These two incidents illustrate how the situations that the ghost tries to create ironically turn out contrary to what he planned. He fails miserably to create any horror or fear and he is, instead, frustrated and humiliated.