Unmarked spoilers are ahead, per Spoilers Off rule.
Some of the Beasts you face are extremely freaky looking or just plain wrong (like a being who is visibly beheaded yet moves as if this were its natural state).
The TurboGrafx-16 port of the first game comes with its own intro, which illustrates Aarbron’s transformation into a monster. First showing him as a man waking up with a start, and then he covers his face with his hands. Moments later his body mutates, and when he lowers his hands we see the face of the iconic monster he was transformed into. All Aarbron can do is let out an anguished, inhuman cry.
Ironically it may come off as quite funny for just how narmy it looks.
The capture of Aarbron‘s sister in the intro of the second game. Imagine being their mother, sitting with her crying baby, when suddenly a flying monster besieges the house, punches a hole through the roof, and reaches a claw through the ceiling to steal your baby. And there is nothing you can do to stop it because the one person who can help you is not home.
The Sega Genesis port creates Nightmare Fuel for the second game with an ending sequence different from other ports — where Aarbron‘s sister is transformed from a monster skull back into a human baby.
The Game Over screens from each of the games are pretty terrifying, especially with the somber music that accompanies them.
The second game shows Aarbron kneeling in a wasteland, his body recoiling as a red beam of light from the sky strikes his chest.
The third game shows Aarbron‘s skeletal remains beside a brook in a wasteland. Though his eyes do not glow red this time, his human skeleton still lies alone. A human skeleton without his clothes or supplies, leaving the implication that he was found and stripped bare, and his corpse was still left behind.
shows Aarbron‘s skeletal remains in a dead forest…but his eyes still glow red. Giving the implication that his soul never passed on and is trapped inside his remains.