Other than Shedinja with Wonder Guard and Focus Sash, which can basically survive anything, a Pokemon can only be immune to three types. These Pokemon are:
>Golurk
Sableye
Spiritomb
Drifblim
Mismagius
Chandelure (Flash Fire)
Gengar
Rotom (Normal)
Jellicent (Water Absorb)
Note, Rotom and Mismagius have the Levitate Ability, so this is why they get a third immunity. Misdreavus should also be on this list, with the Levitate ability. Why did you leave out Misdreavus. ;_;
Also, minus Misdreavus, Rotom and Mismagius any of these Pokemon holding the Air Balloon earns a temporary fourth immunity to Ground. But of course, overall, Shedinja wins. Hooray! :D
And with sixth generation types and new Pokemon, a few Pokemon can be added:
Honedge, Doublade, Aegislash
Mega Gengar
Hope I helped. :)
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