Can Trick-or-Treat and Forest's Curse stack?

Question

I mainly want to know if a Pokemon with one type could gain both Ghost type and Grass type if both Trick-or-Treat and Forest's Curse was used on it, but I also want to know if a Pokemon could have four types if it was a dual typed and had both Trick-or-Treat and Forest's Curse used on it.

Answer 1

Forest's Curse:

It fails if one of the Pokémon's types is already Grass. If the target is under the effect of Trick-or-Treat the Ghost type is replaced by Grass.

Trick-or-Treat:

It fails if one of the Pokémon's types is already Ghost. If the target is under the effect of Forest's Curse the Grass type is replaced by Ghost.

So, in short, No. If Forest's Curse is used, it will make the Pokémon a part-Grass-type, but, when Trick-or-Treat is used, it will make the Pokémon a part-Ghost-type. You cannot use BOTH and make it a part-Grass- and a part-Ghost-type, it's "either-or". So, you'll only get a Triple-typed Pokémon instead of your "Quadruple-typed" Pokémon.