Xavier dropping (most of) his usual idiocy and assholery and successfully fixing the marriage of a caveman couple in "World of Hurt, BC". Possibly the only time Xavier has ever solved a problem without creating a host of new ones.
In "Bloodcorn", a down-on-his-luck farmer attempts to blackmail God into making it rain. When that doesn't work, he goes all out and shoots God, which works, sorta. True, it didn't end well, but still, you have to admire that kind of courage and determination.