An example of satire is when the judge tries to reform Huck’s Pap, demonstrating the naiveté of taking a child from a good home and returning him to an abusive father.
Judge Thatcher seems like a nice guy. When Huck and Tom find the treasure, he keeps it safe for Huck and it even accrues interest. When Huck asks him to keep all of the money, he is surprised but does what Huck asks. He gives his money to the judge so his father won’t take it.
Judge Thatcher, aware of what is happening, tries to give custody of Huck to the widow. Unfortunately, there is a new judge in town.
[He] didn't know the old man; so he said courts mustn't interfere and separate families if they could help it; said he'd druther not take a child away from its father. (ch 5, p. 18)
The judge is convinced that he can reform Huck’s pap, but all he does is make a fool out of the judge by signing a pledge not to drink, then selling the clothes the judge gave him and going off to get drunk.
The judge he felt kind of sore. He said he reckoned a body could reform the old man with a shotgun, maybe, but he didn't know no other way. (ch 5, p. 19)
This is an example of how Twain uses satire because the new judge tried to reform Huck’s father when there was clearly no benefit to doing so. Religion and good intentions are not enough to make someone a better person. This is one of Twain’s most significant points. People do not change.