Shadow Serperior

Shadow Serperior enjoys a stronger offensive presence than its basic forme... to the point where it's about on a par with basic Venusaur. Yeah, this serpent doesn't really put in a lot of work on the PvE side of things.

Best PvE Offensive Moveset

• Vine Whip takes advantage of STAB and is the optimal fast move for Shadow Serperior. 
• Iron Tail trails behind in performance and isn't as useful partly due to lacking STAB.
• Frenzy Plant is objectively great, and the charge move of choice.
• Grass Knot is Serperior's best non-elite charge move and hits hard with STAB.
• Leaf Tornado does get STAB, but has very bad damage output. 
• Aerial Ace is a lackluster move. 

Best PvE Defensive Moveset

• Iron Tail hits quite hard on defense and is more optimal than Vine Whip.
• Frenzy Plant hits for maximum power.
• Grass Knot is weaker, but still usable.
• Aerial Ace and Leaf Tornado perform roughly the same on defense, and are okay as 3-bar moves but don't deal as much damage. 

Vine Whip is the superior pick due to significantly better energy gains along with STAB.

Frenzy Plant is Shadow Serperior's strongest move in a vacuum, as well as in practice. Aerial Ace provides good coverage against other Grass and common Fighting-types, but is generally a weak move. Leaf Tornado is a bad move from a damage perspective, but if you're willing to forgo Aerial Ace's coverage, it can be worth throwing out to fish for debuffs. Grass Knot can technically be run, but it's a significant downgrade over Frenzy Plant.