Before we begin, let me make a confession: I have no clue what a "mangled" modifier would look like. I just thought its inclusion made for a really snazzy title. I suppose if we really wanted to, we could explore whether being mauled by a large predator has an impact on one's ability to formulate proper modifiers, but I don't think that research would end well. If I had just survived a near-death experience with a big ol' grizzly and someone started talking grammar to me, I'd probably punch 'em in the throat. And I'm an English guy.
Dangling modifiers, however, are a very real occurrence in writing, and they can completely destroy the meaning of your sentence. Most people know that an adjective or adverb almost always appears in front of the word it's modifying. If you went around asking, "Have you black my cat seen?" people would probably tell you to get medical help before fleeing in terror. If I said, "My bruise purple hurts," you'll not only be grossed out, but also very confused. Is purple a new kind of pain? Is "purple hurting" more or less intense than "really hurting"? While that kind of construction works in Spanish, we English speakers get all turned around when faced with that kind of construction. The same rule applies to phrases that function as modifiers. Yet sometimes you'll run across something like this:
Dangling from the tree by his suspenders, trouble wasn't far off from Billy Bob Joe.
Even though you can understand it fairly well, doesn't that sentence sound odd? It should. The mind is usually pretty good at catching improper association, which is yet another reason to read your work back to yourself.
Dangling from the tree by his suspenders is all one giant phrase meant to describe poor Billy Bob Joe. When we fail to put it next to him, it's just like talking about our "bruise purple hurting." The phrase ends up modifying the word trouble, which doesn't make a whole lot of sense. Trouble can dangle by its suspenders? Trouble wears suspenders? Oddly enough, if you think about Trouble as the name of a person and re-read the sentence, it makes more sense. Weird, huh? Chalk it up to English.
A corrected version of that sentence would look something like this:
Dangling from the tree by his suspenders, Billy Bob Joe knew trouble wasn't far off.
Unfortunately, these little devils can get really tricky from time to time. This is especially prevalent when dealing with understood subjects. Check out this sentence:
When writing a story, your main character must be a central focus.
At first glance, that sentence doesn't appear particularly malicious. It doesn't jump out and scream at you. It's not particularly hard on the eyes. It's certainly not going to eat your dachshund and wear his fur as a hat. "The understood subject is the reader," you might astutely point out. "The sentence is meant to be instructive. What's wrong with it?"
The brain is great at filling in gaps, and that very strength can sometimes get us into trouble. Your mind automatically associates the understood subject of the first clause (you) and carries that context into the second. If you just think about the phrase "your main character must be a central focus," within the context of authorial advice, it does seem to jive pretty well.
But who's the real subject of the second clause as it's currently written?
Those of you playing at home who said "your main character" win 10,000 Happy Fun Time Points. Yes, the subject in the first clause is understood to be the reader. Congratulations. You've officially become the main focus of this first clause. Isn't that a marvelous feeling?
But when you shift into the beginning of the second clause, the self-referential your can make things ambiguous. That word provides the illusion of a context that isn't there. Even when we continue through the sentence and arrive at main character, the first word has put us in a position where we're not likely to question the subject. It still feels like we, the reader, are the subject. But as it's currently written, that's not the case. Your simply describes the real subject: main character. And we all know your main character doesn't write the story. You do. A revised version of the sentence might read something like this:
When writing a story, you must focus on your main character.
The phrase when writing a story is modifying the situation of the subject (you).
Can it get a little bit tricky from time to time? Absolutely. Just keep in mind where your subjects are, and it will be hard to go wrong. Always make sure that these phrases are followed by the subject they are modifying. No one wants to hear about how your bruise purple hurts.