Here goes.
- Fire - 2x weakness, due to both Grass and Ice being weak to Fire. Dragon's resistance to Fire does reduce the damage however.
- Ice - 2x weakness, due to both Grass and Dragon being weak to Ice. Ice's resistance to itself does reduce the damage however.
- Fighting - 2x weakness, due to Ice being weak to Fighting. Neither Dragon or Grass resist fighting so it remains the same.
- Poison - 2x weakness, due to Grass being weak to Poison.
- Flying - 2x weakness, due to Grass being weak to Flying.
- Bug - 2x weakness, due to Grass being weak to Bug.
- Rock - 2x weakness, due to Ice being weak to Rock. Unchanged.
- Dragon - 2x weakness, due to Dragon being weak to itself. Unchanged.
- Steel - 2x weakness, due to Ice being weak to Steel. Unchanged.
- Fairy - 2x weakness. Dragon is weak to Fairy. Unchanged.
Also, bonus - resistances.
1. It gains a 1/4x resistance to Water since Grass resists Water.
2. It gains a 1/4x resistance to Electric because Grass also resists Electric.
3. It now has a 1/4x resistance to Grass, since Grass resists itself.
4. It now has a 1/2x resistance to Ground, due to Grass resisting Ground.
Tyranitar, Abomasnow, Celebi and others would be so jealous.