What would happen if you used trick-or-treat on a ghost type Pokemon?

Question

If I used trick or treat on a ghost type Pokemon and used a ghost type move (like shadow ball) would the affected Pokemon have a 4x weakness to ghost?

Comments

lol and double STAB

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Similarly to using Forest's Curse on a Grass-type, it will fail.

Answer 1

Trick-or-Treat will fail if the target Pokémon is already Ghost-type.

No, using Trick-or Treat on a Pokemon that is already Ghost type will not make it 4x weak to Ghost type moves.

Source