Ability: Sap Sipper Hydration and Gooey have Grass do 1/2 of the damage, while Sap Sipper makes Grass do no damage, while boosting its attack power as well.
Nature: Rash or Naïve Rash raises Goodra's many Sp. Attacks, but lowers its special defense, which it is by 40 its highest stat (150, follow-up special attack which is 110.) Naive raises Goodra's speed (which, being the lowest, is 80), and lowers it's Sp. Defense..
Sp. Attack: If using Sp. Attack For Type Coverage, Fire Blast (Fire, 110, 85 accuracy, 5 PP, Ice Type Coverage) Blizzard (Ice, 110, 85 Accuracy, 5 PP, Dragon Type Coverage) Sludge Wave/Sludge Bomb(Poison, Wave 95, 10% chance to poison target,Bomb 90, 30% chance to poison target, 100 Accuracy, 10 PP, Fairy type Coverage) If using Physical Attacks for type coverage, then I suggest Sludge Wave, Sludge Bomb, Hyper Beam (not Giga Impact, Goodra has stronger Special Attack then it does Physical) (Normal, 150 damage, 85 Accuracy, 5 PP, however, the user can't move next turn) Muddy Water (Water, 95 in Generation 1-5, 90 in Generation 6+, 100 Accuracy, Hits all targets, Muddy Water does good damage and does not have any recoil effects or damage.)
Physical Attack: If using physical attacks for type coverage: Superpower (Fighting, 120, 100 Accuracy, Ice type coverage, since Goodra doesn't have very good speed, Focus Punch would not be a good move for competitive battling.) Outrage (Dragon, 120 Damage, attacks 3 turns in a row, Dragon type coverage, This attack has disadvantages, judging that it must go 3 turns in a row and you are confused at the end, but not if you have a substitute or the Pokémon as Own Tempo, which is not one of Goodra's abilities) Iron Tail (Steel, 100 Damage, 100 Accuracy, Fairy type coverage.) Even if not using Physical attacks for type coverage, I would not change the moves, since they are all pretty powerful. The only thing I would change is Outrage to Power Whip, since it has equal damage. Power Whip is a Grass type move with 85 accuracy and no recoil stats or damage.
Stat Move: Substitute (Normal, -- Accuracy, replaces the user with a substitute that keeps them from taking damage with however much HP the user uses on the substitute. You can use moves while it is substituting, and you can heal Goodra while the substitute is out.) Attract (Normal, -- Accuracy, the user makes the Pokémon fall in love with it if it is the opposite gender, and this almost always ''immobilizes the user with love'', which, like paralysis, keeps it from attacking. You can use this time to heal Goodra.) Curse (Ghost, -- Accuracy, Ghost-type Pokémon use 50% of their maximum HP to place a curse on the target. The cursed Pokémon loses 25% of their maximum HP every turn. If the user has less than 50% HP remaining, they will faint but the curse still takes effect. I'm not 100% sure, but this does not take Goodra's health. If it does, Attract or Substitute should be included in the move set. )
Use the last available move with Acid armor. Acid armor has 40 PP in generations 1-5, and 20 in generation 6+. Acid Armor sharply raises Goodra's attack stat (+2 stages each), and Goodra's special defense is very high as well, making this move stronger. Although, this is an Egg Move, so it would be difficult to achieve this move. If you can't get Acid Armor, I suggest Fire Blast. It would be a 2nd Sp. Attack and gives more type coverage, which is a plus.
I hope you like this moveset! If you want a definite moveset, then I suggest:
Thanks for reading this comment if you think I should have done something different or if this moveset helped you :D