Shadow Vileplume

Shadow Vileplume is actually a surprisingly strong Grass or Poison Type attacker, though not the best. If you happen to find a high-IV Shadow Vileplume, then it can definitely perform. However, it's inferior to numerous other Pokemon that fill the same roles.

Best PvE Offensive Moveset

• Razor Leaf pairs well with Solar Beam to fulfill a Grass-type role. 

• Solar Beam is superior to Petal Blizzard due to its massive base power.

• Acid shares same typing with Sludge Bomb to let Shadow Vileplume function as a Poison-type. 

• Moonblast has no place on an offensive Shadow Vileplume.

Best PvE Defensive Moveset

• Razor Leaf is generally preferable for its high base damage.

• Acid is inferior in damage output, but is less likely to be resisted by Dragon-types. 

• Sludge Bomb performs best on defense thanks to its earlier damage window and being a 2-bar move.

• Petal Blizzard is better than Solar Beam for defense due to an earlier damage window.

• Moonblast can offer some coverage against Dragon-types, but is less likely to be used as a 1-bar move. 

Razor Leaf is preferred for hits high STAB damage output at the cost of having the worst energy gains in PvP. Acid gets STAB and can be useful in some niche situations against Grass or Fairy-types, but has below average energy gains. 

Sludge Bomb is the primary and (most of the time) only charge move used by Vileplume due to its lesser energy cost compared to Vileplume's other charge moves. The very poor energy gains from Razor Leaf often risks Vileplume fainting before being able to utilize its more expensive charge moves. Moonblast is preferred for its coverage against common typings.