Question

Which are the Pokemon that are immune to Jigglypuff's singing?

Comments

Do you mean in-game Sing or Jigglypuff's singing in the anime?

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In the anime

Answer 1

Is immune via Vital Spirit:
Mankey
Primeape
Delibird
Vigoroth
Lillipup
Electabuzz
Magmar
Tyrogue
Elekid
Magby
Electivire
Magmortar

Is immune via Insomnia:
Drowzee
Hypno
Mewtwo
Mega Mewtwo Y
Hoothoot
Noctowl
Spinarak
Ariados
Murkrow
Shuppet
Banette
Honchkrow
Delibird
Gourgeist
Pumpkaboo

Is immune via Soundproof:
Voltorb
Electrode
Mr. Mime
Whismur
Loudred
Exploud
Mime Jr.
Shieldon
Bastiodon
Snover
Abomasnow
Bouffalant

Comments

You have a better answer than me. I'll up vote :)

Answer 2

All Pokemon with the ability Soundproof, Vital Spirit or Insomnia are able to block the move Sing.

Hope I helped.