When I read this question the first lie that came to my mind was Tom’s lie that he was helping rescue Jim. There are many other lies in the book, but this one always bothers me. I always thought of Tom as basically a good kid, but this is horrific.
Tom knows that Jim has been freed, but he goes along with Huck’s plan to free him. Tom loves adventure and fun, and he is only interested in the scheming he can do to “free” Jim, even though what he is doing is potentially dangerous to Jim, Huck, and even Tom.
Huck cannot believe it when he finds out that Jim actually is free.
I asked him what was his idea, time of the evasion?—what it was he'd planned to do if the evasion worked all right and he managed to set a nigger free that was already free before? (Ch 41, p. 193)
Tom’s answer is that they would go off with Jim and have adventures. This further demonstrates that Tom is not grounded in reality. Everything is a game with him.
Tom’s game has real-life consequences. Tom is shot in the escape, and Jim risked being hanged until Tom reveals that he actually is free. Therefore Tom not only caused great injury to himself, he might have gotten Jim killed.