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Nightmare Fuel: Digimon Frontier
The climax of the Mercurymon arc has Mercurymon nearly stuffing Takuya into a coffin and killing him.
As hilarious as his voice acting is, there's just something chilling about how playfully murderous IceDevimon is. Even worse, his dialogue implies that those... things in the basement of Cherubimon's castle were the result of him feeding on the data of Digimon that he captured.
Duskmon is actually a pretty brutal Deconstruction of the Adventure series. Take a random human child with strong emotions, drag him into your world against his will, and make him fight for you.