The Headless Horseman, of course. It's like the Terminator, but as a ghost; it cannot be bargained or reasoned with, you can't run from it and hope to escape, and it feels no fear, pity, remorse, or hesitation. It's just coming to take your head and there's little you can do but delay the inevitable, and you won't know why it's come for you.
Christopher Walken's performance as the Headless Horseman deserves a special mention. It's considered one of his finest performances, and he really gets across what a monstrous butcher the Horseman was in life.
He kills Beth Killian and her husband, but not their son Thomas, and we get a Hope Spot as he begins to leave and Thomas is left hiding beneath the floor. Then, suddenly, the Horseman stops, turns as if he angrily realizes he's forgotten something and starts taking his axe to the floor. We're treated to a shot of Thomas cowering beneath the floorboards as they start to get bashed in, and then when he tries to run, he gets grabbed by the Horseman. We, fortunately, get a Gory Discretion Shot and don't have to see what comes next.
Oh, worse than that. Just before, after Beth is decapitated, we don't see the beheading, but her head rolls and her lifeless eyes seem to stare at her son through a gap in the floorboards before the Horseman finally (mercifully) collects it.
As Ichabod and Brom flee the Horseman after attacking him, they run across a covered bridge and hear the Horseman's footsteps on the planks. They stop at the end, turn to face him...and see nothing, but continue to hear him walking across the bridge. A scuff and a bit of dust draws their attention up, but it's too late. The Horseman drops down behind them.
When Brom tries to fight the Horseman, he seems to be doing okay against him, before the Horseman catches him off-guard and brutally bisects him through the waist.
The deaths in the church scene, particularly because of how quickly they happen. During the chaos, Doctor Lancaster tries to confess Lady Van Tassel's conspiracy, only for Reverend Steenwyck to bash his head in with a crucifix, followed by Baltus shooting him in a moment of panic. Then, barely seconds after Baltus tells everyone present that he intends to find out what's going on, the Horseman proves that holy ground isn't as much of an obstacle as everyone hoped.
The townsfolk take shelter in the church and the Horseman cannot step on the holy ground, so it seems for the moment that his wrath is averted. As chaos erupts in the church, we see the Horseman break off a fence post and retrieve a coil of rope. When Baltus stands on the church altar and declares he will reveal what is happening, the window behind him suddenly shatters and the pointed tip of the fence post bursts through his chest. The Horseman then uses the makeshift harpoon to yank Baltus out the window and across the church grounds until his head breaks through the fencing, allowing the Horseman to take his head.
Ichabod's flashbacks, especially the last one. To wit: Young Ichabod enters his father's secret torture chamber, drawn by his mother calling for him...from inside an iron maiden, where her eyes lifelessly stare out at him. Clearly scared out of his mind, he ends up injuring both of his hands on one of the torture implements. Then the iron maiden opens and Lady Crane's mutilated corpse falls out, accompanied by a massive flood of blood.
Just the sight of the Horseman with his head returned to him. We have no actual reason to think the danger has passed, and if anything, the sight of him fully restored and never once shown blinking makes one think he's going to be more dangerous.
Lady Van Tassel's Dragged Off to Hell death. Right after the Horseman savagely kisses her and tears her lips with his teeth (while possibly also biting out her tongue!) he rides back into the Tree of the Dead, taking her with him in a fountain of blood while she shrieks in agony. Once the roots of the tree settle back down again, all that's left is her hand sticking out of the tree — and as Ichabod watches in disgust and horror, her muscles relax in death and her fingers curl upwards, as if she's beckoning...
