An Oddish, huh? I was expecting to see someone whip out a Water-type to take advantage of the river, but I guess not.

Fortunately for us, Terrorform, Grass-types don't have very many moves that can destroy multiple Double Team images with a single attack... so do just that. Vine Whip's one of them, but fortunately for us here Fireguardian has forgotten that Oddish doesn't know Vine Whip. So it looks like he'll be wasting a turn there.

Bathe the Oddish in Flamethrower and incinerate the weed and his Poisonpowder with a Fire Blast.

Double Team, Flamethrower, Fire Blast