All season long, we were wondering if “Serial” was going to get a Saturday Night Live parody. Can a podcast get that big? This week’s SNL proved, yes, it can. And it’s a good thing, since it was pretty damn great. Unlike the Funny or Die “Serial” sketch from last week, SNL’s sketch doesn’t feel like just a run-through of inside jokes and memes — they actually turn it into something new, in turn heightening the comedy. Also, the impressions are seriously well-written and -performed. What it comes down to is, um, Christmas magic.