The Title
The title of the story is an example of irony because it is entitled How the Grinch Stole Christmas. Of course, the Grinch does not actually succeed in his attempt to steal Christmas, and indeed ends up celebrating with his Who community.
CIndy-Lou Who
When Cindy-Lou Who catches the Grinch in the middle of his theft, it is a moment of dramatic irony. The reader knows that the Grinch is not really Santa Claus, but Cindy-Lou Who thinks he is taking their Christmas tree to get fixed, rather than stealing it. The moment emphasizes Cindy-Lou Who's innocence and inquisitive nature.
Santa Claus
Though the Grinch becomes a type of reverse Santa Claus by sneaking into Who houses and stealing their presents, at the end of the story, his role shifts. He returns to Who-ville with everything he stole, effectively becoming an actual Santa Claus for the people of Who-ville.
The Scheme
Although the Grinch sets out to destroy Christmas, he later joins in on the festivities. He even hands out gifts to all the children, becoming an embodiment of the festive spirit.
