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Jason is a polite person who is sometimes very kind and Johnny is a Jerkass.
Justified: There is a stimulant in the potion which drives Jason into an unstoppable rage.
Inverted: Johnny drinks a potion that transforms him into a human named Jason.
Subverted: Jason drinks the potion and finds that the stimulant doesn't effect him.
Double Subverted: ...Until it has totally absorbed into his blood.
Upon even smelling the fumes of the potion, Johnny goes on a violent killing rampage.
The Hyde personality is a different gender.
Zig Zagged: The potion has to be drunk in either the correct place, at the correct time, or with the correct temperature, to have any effect. Jason spends weeks trying to find out what the correct place/time/temperature actually is
Averted: Jason did not became Johnny.
Lampshaded: "Did Jason seem a little....completely opposite to you?"
Defied: Either Jason refuses to drink any concoctions that will turn him into Johnny or Jason turns into Johnny permanently.
Played For Laughs: Frank wants to protect Jason from Johnny, the monster. And both hide in odd places where inexplicably Jason disappears, and Johnny appears.
Played For Drama: Jason keeps convincing himself that he needs Johnny's strength or determination to overcome so challenge in his life, but each time he drinks the potion he loses control and there is a corpse in front of him when the potion wears off.