When two allies attempt to use Grass Pledge and either Fire Pledge or Water Pledge on the same turn, the ally moving first will not itself use a move, but instead the ally moving second will use a combined attack with a power of 150 and an additional effect immediately after it:
If Grass Pledge and Fire Pledge are used in the same turn, the ally moving second will use Fire Pledge with a power of 150, and create a sea of fire on the target's side of the field for four turns. The sea of fire damages all non-Fire-type Pokémon on that side of the field for 1/8 of their maximum HP at the end of each turn.
If Grass Pledge and Water Pledge are used in the same turn, the ally moving second will use Grass Pledge with a power of 150, and create a swamp on the target's side of the field for four turns. This swamp quarters the Speed of all Pokémon on that side of the field.
Grass Pledge, Fire Pledge, Water Pledge
It will do the damage of whatever Pledge was used last. If Grass Pledge is used after Water Pledge, it will quarter the Speed of all Pokemon on the other side of the field. If Water Pledge is used after Fire Pledge, the chance for secondary effects is doubled. If Fire Pledge is used after Grass Pledge, all non-fire Pokemon affected will have 1/8 of their max HP taken away at the end of every turn.