[Battle] How to make a powder move attack not hit any grass types?

[Lord Shobby]

I'm trying to add a few new moves into the game, including a grass type Explosion clone with the powder move flag. The problem is that, as is, it's only blocked by one grass type on the field at a time. Equipping Safety Goggles on an ally Pokemon doesn't work either. Here, you can see the ally Poochyena with goggles equipped fainting, and the Lotad fainting as well - even though the Seedot is immune and displays the "it doesn't affect" text.

Is there anything I need to change with the Explosion code in order for this move to work properly?