Does your WIP have a big problem with multiple repetitions of big?
If you search Google for "most overused words in writing," big will appear on the majority of lists you find. This post provides alternatives.
100 Ways to Say "Big"
I found some of your advice puzzling. Take this pair of sentences:
Bernard's ego was bigger than his bank account.
Bernard's ego outmatched his mammoth bank account.
You said the second was better because it uses an active verb and a reader might misunderstand the first. I find that hard to believe. The formula "A's x is bigger than his y" is an English idiom, along with other stock variations like "His ambition outstripped his abilities." Most people would've heard it or used it and its variations many times.
I also don't think the comparison works because
outmatched implies a competition between his ego and his bank account, when the first sentence was only making a point about the size of Bernard's ego.
Outmatched works better with "His lifestyle outmatched his bank account," or some such, though it's a different point about Bernard's character. The modifier
mammoth only adds to the imbalance. If you have to describe the object of the comparison, you lose the pithiness of the idiom. Adding
mammoth is like saying "His ego outmatched his bank account, which was very large by the way." We have to know the size of his bank account before the comparison is made for the idiom to work.
Then there's this pair:
The big tiger moved silently through the grass.
The behemoth tiger stalked silently through the grass.
Behemoth is a noun meaning "the largest and strongest thing," not an adjective, and I've never seen it used as a premodifier (M-W's "a behemoth truck" notwithstanding). It's usually used as a descriptive stand-in for a preceding noun (the technical term escapes me at the moment): "I saw the tiger again. This time the behemoth [= the tiger] was coming for me."
Silently adds something to
moved, but nothing to
stalked because to stalk (in its transitive form) means "to pursue by stealth" (= silently). Of course,
stalked has no direct object in your example, making it intransitive. The intransitive meaning of stalked, however, is different from the transitive meaning: "The tiger stalked the man [trans. = pursued stealthily]" but "The tiger stalked away [intrans. = walked slowly and softly/walked away stiffly, sullenly]." So
stalked can't be substituted for
moved silently without giving it an object or changing the meaning of the sentence.
In many of the other examples I wondered why you didn't recommend striking out big altogether, instead of replacing it with a synonym. Take the "big bruise" example. You have a modifying phrase describing the bruise as impossible to hide (= big). Once you have that description, calling it big (or anything else) seems redundant.
