Confusion about how certain field effects works

[Hakimblue99]

I noticed that some field effects have effects like this listed under them:

X type moves deal additional Y type damage or something like that.

 

Example:

Corrosive field

Grass type moves deal additional Poison type damage

 

My question is...how the heck does that work? Does it change the move from grass to poision type? Or does it became a grass/poison move? If the latter's the case then how will  it work?

 

If I used a grass move in a corrosive field on a poison/water type, how will the type effectiveness be calculated?

 

Sorry if the question sounds silly, or has been asked before. I'm kinda new to this community.

 

[wcv]

Just now, Hakimblue99 said:

I noticed that some field effects have effects like this listed under them:

X type moves deal additional Y type damage or something like that.

 

Example:

Corrosive field

Grass type moves deal additional Poison type damage

 

My question is...how the heck does that work? Does it change the move from grass to poision type? Or does it became a grass/poison move? If the latter's the case then how will  it work?

 

If I used a grass move in a corrosive field on a poison/water type, how will the type effectiveness be calculated?

 

Sorry if the question sounds silly, or has been asked before. I'm kinda new to this community.

 

Look up the move Flying Press, which is from the canon games and is both fighting and flying type.

[CMV]

Presumably:

 

Grass move vs Poison type - 0.5x multiplier (not very effective)

Grass move vs Water type - 2x multiplier (super effective)

Poison move vs Poison type - 0.5x multiplier

Poison move vs Water type - 1x multiplier (normal effectiveness)

 

Overall effectiveness: 0.5 x 2 x 0.5 x 1 = 0.5