Generally Benign

This is a wonderful story. I love that it's completely realistic and believable, which makes the monster believable, too. Its very understated quality is what makes the ending so chilling. It has a great sense of its time and place, too-- something I always admire. Great read.

Hi Cody,

Some of my feedback, all my opinion only:

Livestock - it would be nicer if you were more specific here, for the reader's benefit. Particularly as you describe an individual mutilation. "Cattle mutilation" works, and makes the horse reveal later more crisp.

Great Descriptions:
hot-dog style
lip-gloss slicked mouth (i can imagine the close up)

"It could have been Satanists or aliens maybe... etc" - this sentence gets quite long and clumsy, can you chop it up?

"but spared the lush fields" - I think you've omitted some prose here, maybe needs to be reversed to the "but the lush fields had been spared."

"We weren’t losers" - cut this, too much telling. You're already showing the boys, so just let the reader decide.

"Mirror images from different times, one young and one older, screaming and
punching the other for ruining their own life." - I like this whole Pat and Pat's dad description, felt really genuine. This sentence needs some polishing though.

Long lists:
Consider dropping a few items or else your lists will be so long that they distract too much from the actual story:

•  "summer camp, merit badge rallies, the Klondike Derby, hiking trips, or spring camporee"
• "... we were packing the trailer with grills and sleeping bags and first aid kits and tents and coolers"

Your descriptions are vivid and nice, but often seem to take too much leave from the narrative. It's  kind of jarring, especially when something in the present reminds the MC of something in the past, and they describe in detail the thing from the past.
Example, Pat at the creek. There's some creature approaching/attacking and we have barely any idea what it is/looks like and you drop this:

He probably thought of the bear mace at the bottom of his backpack (that parts fine), or the pocketknife he bought at the Indian powwow at the middle school three years before that he wasn't allowed to take anywhere but camping (umm.. what's happening with the bear thing??)

What I would have peferred is something like "He probably thought of the bear mace at the bottom of his backpack, and wondered if it would have any effect on the _SOME_PHYSICAL_DESCRIPTION_OF_THE_CREATURES_CHARACTERISTICS_ here.

You do go on to describe the creature after the event, but by then it's too late to really understand and I needed to re-read.

It's ok to be vague on creature details when they're lurking in the shadows, but if they're in plain sight and murdering people it's good if we know what they look like so we have some idea of what action is taking place. At least something to compare it with, if you don't want to be too specific. humanoid, bloblike, lizardesque etc.

You have a good plot here. Pat and the MC are both believable, consistent characters. The "Bear that's not a bear" tale is told right, with enough foreshadowing that the reader knows it's not really a bear, but still has to wait until the end to find out the reality.
You write some excellent descriptions and make good use of all the senses particulalry touch and smell. Just be careful about over-describing minor details in spite of major plot events.
Some of your paragraphs would also benefit from being split so that the reader can detect changes in location/POV/time.

Hope this helps.