I would say one of the best examples of satire in the end of the book is Tom’s “rescue” of Jim. Huck arrives at Tom’s aunt’s house and pretends to be him when she thinks he is Tom. So he stays. When Tom arrives, he develops a complicated scheme to free Jim. Although the over-intricate and ridiculous plan smacks of The Adventures of Tom Sawyer juvenilia, it’s also an excellent satire on some of the base beliefs in slavery.
“Well, if that ain't just like you, Huck Finn. You can get up the infantschooliest ways of going at a thing. Why, hain't you ever read any books at all?— Baron Trenck, nor Casanova, nor Benvenuto Chelleeny, nor Henri IV., nor none of them heroes? (ch 35, enotes etext p. 159)
By this time, Huck genuinely believes that Jim is a person and he is trying to help him as a friend. Tom, on the other hand, sees Jim only as a pawn in the game.
“I mean every word I say, Aunt Sally, and if somebody don't go, I'll go. I've knowed him all his life, and so has Tom, there. Old Miss Watson died two months ago, and she was ashamed she ever was going to sell him down the river, and said so; and she set him free in her will.”
“Then what on earth did you want to set him free for, seeing he was already free?”
“Well, that is a question, I must say; and just like women! Why, I wanted the adventure of it; and I'd 'a' waded neck-deep in blood to—goodness alive, AUNT POLLY!” (ch 42, p. 190)
The fact that Tom would never have helped free Jim if he had not already been freed gets to the heart of the issue. It would never occur to Tom to tell Huck that Jim is a free man. He just enjoys the game. He does not see what he is doing, planning the overly complicated and dangerous escape, as morally wrong. Rather, he would think it was morally wrong to try to help Jim escape in earnest. Huck’s morals and Jim’s morals are now complete polar opposites. This shows how far Huck’s moral code has strayed from society’s. Twain uses satire to show how ridiculous society's code really is.