The entire Ghost of Christmas future scene, involving Scrooge being chased by his own funeral wagon, driven by a literal pair of Night Mares (complete with Red Eyes, Take Warning).
The death scene of the Ghost of Christmas Present. Arguably the most disturbing and faithful scene to the original novel than in any other adaptation.
On that note...Ignorance and Want.
When Want is shown as a grown-up woman (most likely a prostitute), she is strapped in a straightjacket and dragged away screaming.
The whole scene with Jacob Marley. He's introduced by throwing his ghostly safes through Scrooge's door, he floats in midair, his eyes rarely focus - and that's just his general appearance. He's constantly scaring Scrooge (and the audience) by screaming and howling, and at one point he dislocates his own jaw and, still needed to vent his anger, he jerks it up and down with a whole lot of cracking sounds. Eeeeeesh.