>>47114385Pokemon should have negative effectiveness, and Water should be negatively effective against Grass (meaning Grass-types heal when hit by water moves).
And because that makes the types unequal, just abandon Grass as a starter type. It doesn't fit in with the other 2. Fire and Water are elements, while Grass is alive. And Fire and Water are built for standard play (using attacks and taking attacks) while Grass is built for spreading status.
Maybe make Ice strong against water so that Fire, Ice, and Water can be a type trio (like in Club Penguin) and have Grass be just another type rather than a starter type.