Farmer Yoon is not alone, and I don't mean that as a terrible lead-in to he's got you, best friends forever!
I've noticed this a few times on the inn-to-farm run my sad, neglected alts make most days. There's something shadowy on Sunsong Ranch, right by Yoon himself.
It's a little easier to see in-game because it's moving, but hopefully you can make out the slight shadow in that screenshot, between the witchberries and the carrot.
Investigating this proved difficult. As soon as you cross into the phased part of Halfhill, the ranch itself, the shadow despawns. It despawns more quickly than Flying Serpent Kick can handle, which is saying something. That skill can handle most things.
My investigation tailed off, until my most recent silliness reminded me that I have a priest, and that priests have Mind Vision. What better way to investigate the haunting of Sunsong than with the Yoon cam?
Welp, that there's a ghost alright.
I think the obvious explanation for this one is that Yoon's late grandfather is there at Sunsong Ranch with him, observing Yoon's time on the farm and growing increasingly twisted and evil.
What? Remember Grandpappy Yoon is the farmer so epic he saved all of Halfhill. Now his supposedly-farmer grandson, the one he left his beloved farm to, is wearing the cleanest overalls known to farmerkind and stands about being a darn citypaw while everyone else does the work for him. It's enough to drive any self-respecting Tiller to poltergeistdom.
Choice quotes from the sedentary grandson:
How am I supposed to succeed at this whole FARMING thing if I can't even clear my farm for planting?
I know the difference between a carrot and a turnip! One's orange and one's white, after all!
Take over for me... uh... what's your name? I need a break. You can find me in my house if you need me.
For shame, Farmer Yoon. It's really no surprise your grandfather now occupies the same form as the Restless Shadeling and the ghoul from the Haunted Memento. The guy looks furious even when he's trying to be friendly:
No more waves, please, Grandpappy Yoon. I think I'd have been better off never knowing that you're still around.