Branching out from the original class, I wanted to show a different type of fear, and the way the boggart can show fears you don't even realise yourself.
George grins at his brother as they saunter casually through the Hogwarts halls. They are up to no good. Not that that is anything unusual, but this time their only real target is themselves. This time they are going boggart hunting.
The story of Neville's cross-dressing Snape-boggart had spread through the school like wildfire. And while none of the others had the same universal appeal, tales of the other students' attempts had cemented the lesson and professor as one of the best in years. He and Fred had tried to convince Professor Lupin that all of the students deserved such a valuable opportunity, not to mention the humour potential, but to no avail. Apparently as fifth year students there was simply too much work needed to catch them up to OWL level.
So the Troublesome Twins had decided to take matters into their own hands. They had been reliably informed that the boggart was still trapped in a case in the Defence professor's office, so they decided to face it themselves. It would mean breaking into a teachers office, but that's just a bonus; another one for the list.
They come to a stop outside the office, and Fred nods at him before moving to lean casually against the wall, eyes alert. Perhaps they should have brought the Map for something like this, but they wanted a challenge. And where is the fun without a little risk?
A whispered spell later and George slips into the room, closing the door carefully behind him. Looking around, he approves of the new office design; it fits with what he has seen of the professor so far. Gone are the blinding self-portraits of the previous occupant, replaced instead with well-worn books, a tank sitting so-far empty in one corner. The furniture is all standard-issue, and the office supplies are cheap and worn, but the overall atmosphere is one of quiet studiousness; a welcome change to past years.
Initial survey complete, George turns his focus to the battered case sitting against one wall. It rattles for a moment, and he realises that this must be it. The boggart. Grotesque figures flash through his mind as he wonders what form it will take; all joking aside, he really doesn't have a clue. Taking a deep breath he positions himself before it and aims his wand.
"Alohomora." The case opens, a dark cloud bursting out, swirling for a moment before coalescing into the shape of his deepest fear. Black robes swirl and then still, a Gryffindor crest appearing on the breast. Pale skin, spattered with freckles. A flash of red turns into flaming hair. Finally, a face emerges, one he recognises in an instant.
"Fred?" This doesn't make sense. Why would his twin be his greatest fear?
In confusion, he turns to ask his brother's opinion. He freezes, a jolt going through him as he looks at the empty space where he expected to see the familiar form of his twin. A moment later he shakes himself, berating his jumpiness. Of course Fred is not there, he is out in the corridor keeping watch, just as they discussed.
A sudden thought, and he steps closer to the unnaturally still boggart, examining it carefully. The face is familiar, yes, but it is not quite as he thought; there are subtle differences in the shape, the pattern of freckles. Then he looks at the eyes. They are not bright and laughing as they should be, instead they are lost, empty, broken.
He backs away in horror as realisation crashes through him; unable to face the indescribable pain of the possibility it shows.
His boggart is not Fred, it is himself. Alone.