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A few people mentioned 'duo' pokemon, and I've seen a potential opportunity.
There is a symbiotic relationship between sea anemones and clownfish in the Great Barrier Reef. Clownfish are one of the few creatures that are unaffected by the poisonous stingers of the sea anemone.
I think there's potential for Zangoose/Seviper duo. The Water-type clownfish would have Immunity, and the Poison-type anemone would have Poison Point.