Here's a good Assault Vest Set for Goodra:
Trait: Sap Sipper
EVs: 252 HP / 252 Sp. Atk / 4 Sp. Def
- Draco Meteor / Dragon Pulse
- Fire Blast
- Sludge Bomb
- Thunderbolt / Muddy Water
This set is pretty basic.
You can use Draco Meteor for the immediate power, but it forces you to switch out because of the Sp. Atk drop. Dragon Pulse is a good alternative for avoiding the side effects, but has less power.
Fire Blast is coverage and hits Steel-types that Goodra struggles with. Flamethrower could also be an option if you're worried about accuracy.
Sludge Bomb deals with Fairy-types, such as Florges, Azumarill, and more.
Here you have another choice between Thunderbolt and Muddy Water. Thunderbolt deals with bulky Water-types, while Muddy Water can deal with Ground-types and Fire-types. It's your choice.
Anyways, I hope I helped!