What are some examples of satire in "Huckleberry Finn"? What did Mark Twain choose to discuss seriously?
Tom's plan to help Jim escape.
At the end of the book, Twain recounts Tom Sawyer's plan to bust Jim out of his "prison." Tom repeatedly makes the plan unnecessarily complicated, merely for the boyish "excitement" of it. The reader becomes annoyed with Tom while still laughing at his immaturity, so the satire worked.
However, Twain discusses the slavery issue seriously. Jim is in real danger throughout the book, and Twain never makes light of that danger.