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2 expanded on Tolkien Immortality, added caveat about non-authoritativeness of explanations given
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I've seen three (4, now that I've seen harlandski's Gygax quote) reasons for Elves being immune to a Ghoul's paralysis ability:

Positive Energy

Per the Gygax quote, elves are suffused with positive energy, rendering them immune to the negative energy which powers a Ghoul's paralysis.

Tolkien Immortality (and historical inertia)

Apparently, an old source book (PC1: Tall Tales of the Wee Folk Pg 24) states that Ghouls' paralysis is caused by the victim's fear of death; Elves (who are immortal, in the Tolkien Immortality "can't die of old age" sense) thus have a sufficiently different vision of death that they're immune. (source)

Historical Inertia

Chainmail, on which D&D was (in large part) based, made Elves immune to Ghoul paralysis as a balance mechanic: Ghouls were cheap, Elves were expensive, and the immunity prevented Ghouls from zerg-rushing Elves. (source)

Pathfinder Lore

In Golarion (the default Pathfinder setting), the first Ghoul was an Elf, and the elven immunity to their paralysis is a manifestation of that.

The fact that elves have an unusual immunity to this paralysis is curious indeed, but most point to Kabriri’s form (and to the almost elven features of most ghouls) as the answer. They say that before he succumbed to his cannibal urge and became a demon, Kabriri himself was an elf. The long ears and slender bodies that most ghouls develop, despite their original race, is thus an echo of Kabriri’s legacy—and the fact that their paralytic hungers have no effect on elves is but another manifestation of this strange bit of history.

(source)


Significant Limitation/Caveat: all of these sources are second- or third-hand, and some are definitely retroactive and/or campaign-world-specific explanations.

I've seen three (4, now that I've seen harlandski's Gygax quote) reasons for Elves being immune to a Ghoul's paralysis ability:

Positive Energy

Per the Gygax quote, elves are suffused with positive energy, rendering them immune to the negative energy which powers a Ghoul's paralysis.

Tolkien Immortality (and historical inertia)

Apparently, an old source book (PC1: Tall Tales of the Wee Folk Pg 24) states that Ghouls' paralysis is caused by the victim's fear of death; Elves (who are immortal, in the Tolkien sense) thus have a sufficiently different vision of death that they're immune. (source)

Historical Inertia

Chainmail, on which D&D was (in large part) based, made Elves immune to Ghoul paralysis as a balance mechanic: Ghouls were cheap, Elves were expensive, and the immunity prevented Ghouls from zerg-rushing Elves. (source)

Pathfinder Lore

In Golarion (the default Pathfinder setting), the first Ghoul was an Elf, and the elven immunity to their paralysis is a manifestation of that.

The fact that elves have an unusual immunity to this paralysis is curious indeed, but most point to Kabriri’s form (and to the almost elven features of most ghouls) as the answer. They say that before he succumbed to his cannibal urge and became a demon, Kabriri himself was an elf. The long ears and slender bodies that most ghouls develop, despite their original race, is thus an echo of Kabriri’s legacy—and the fact that their paralytic hungers have no effect on elves is but another manifestation of this strange bit of history.

(source)

I've seen three (4, now that I've seen harlandski's Gygax quote) reasons for Elves being immune to a Ghoul's paralysis ability:

Positive Energy

Per the Gygax quote, elves are suffused with positive energy, rendering them immune to the negative energy which powers a Ghoul's paralysis.

Tolkien Immortality (and historical inertia)

Apparently, an old source book (PC1: Tall Tales of the Wee Folk Pg 24) states that Ghouls' paralysis is caused by the victim's fear of death; Elves (who are immortal, in the Tolkien Immortality "can't die of old age" sense) thus have a sufficiently different vision of death that they're immune. (source)

Historical Inertia

Chainmail, on which D&D was (in large part) based, made Elves immune to Ghoul paralysis as a balance mechanic: Ghouls were cheap, Elves were expensive, and the immunity prevented Ghouls from zerg-rushing Elves. (source)

Pathfinder Lore

In Golarion (the default Pathfinder setting), the first Ghoul was an Elf, and the elven immunity to their paralysis is a manifestation of that.

The fact that elves have an unusual immunity to this paralysis is curious indeed, but most point to Kabriri’s form (and to the almost elven features of most ghouls) as the answer. They say that before he succumbed to his cannibal urge and became a demon, Kabriri himself was an elf. The long ears and slender bodies that most ghouls develop, despite their original race, is thus an echo of Kabriri’s legacy—and the fact that their paralytic hungers have no effect on elves is but another manifestation of this strange bit of history.

(source)


Significant Limitation/Caveat: all of these sources are second- or third-hand, and some are definitely retroactive and/or campaign-world-specific explanations.

1
source | link

I've seen three (4, now that I've seen harlandski's Gygax quote) reasons for Elves being immune to a Ghoul's paralysis ability:

Positive Energy

Per the Gygax quote, elves are suffused with positive energy, rendering them immune to the negative energy which powers a Ghoul's paralysis.

Tolkien Immortality (and historical inertia)

Apparently, an old source book (PC1: Tall Tales of the Wee Folk Pg 24) states that Ghouls' paralysis is caused by the victim's fear of death; Elves (who are immortal, in the Tolkien sense) thus have a sufficiently different vision of death that they're immune. (source)

Historical Inertia

Chainmail, on which D&D was (in large part) based, made Elves immune to Ghoul paralysis as a balance mechanic: Ghouls were cheap, Elves were expensive, and the immunity prevented Ghouls from zerg-rushing Elves. (source)

Pathfinder Lore

In Golarion (the default Pathfinder setting), the first Ghoul was an Elf, and the elven immunity to their paralysis is a manifestation of that.

The fact that elves have an unusual immunity to this paralysis is curious indeed, but most point to Kabriri’s form (and to the almost elven features of most ghouls) as the answer. They say that before he succumbed to his cannibal urge and became a demon, Kabriri himself was an elf. The long ears and slender bodies that most ghouls develop, despite their original race, is thus an echo of Kabriri’s legacy—and the fact that their paralytic hungers have no effect on elves is but another manifestation of this strange bit of history.

(source)