Shadow Venusaur

Shadow Venusaur is a decent source of Grass Type damage, beating even Mega Venusaur in raw DPS when not counting Mega Boosts. However, Shadow Venusaur is much more frail and requires dodging to mitigate incoming damage, and it doesn't provide a damage boost to every player like Mega Venusaur does. Shadow Venusaur is definitely a decent investment if you need improved Grass Type performance and don't already have an army of Kartana ready to go.

Best PvE Offensive Moveset

• Vine Whip is on par with Razor Leaf on attack; though they’re very different moves, they end up close in cycle DPS.
• Frenzy Plant has absurdly high damage for a 2-bar charge move and is optimal. 
• Solar Beam is frequently superior to Petal Blizzard due to its massive base power.
• Sludge Bomb has little use on an offensive Shadow Venusaur.

Best PvE Defensive Moveset

• Razor Leaf is far superior to Vine Whip, netting higher damage and energy gain.
• Sludge Bomb is an off-type multi-bar charge move, which can hurt Shadow Venusaur's counters.
• Frenzy Plant is powerful but has poor typing and is easily dodged.
• Petal Blizzard is the hardest to dodge, but doesn't get used often as a 1-bar move.
• Solar Beam is too slow for defense. 

Vine Whip is the preferred fast move for Venusaur due to greater energy generation, which allows Venusaur to take advantage of its powerful charge moves. Razor Leaf is a more polarizing fast move that focuses on dealing damage without requiring energy or being denied by shields, though its slow energy generation causes Venusaur to lose some neutral matchups. 

Frenzy Plant is the main selling feature of Venusaur, with an insane 2.22 DPE (Damage Per Energy) and moderate energy cost. If you don't have access to Frenzy Plant, consider Ivysaur with Power Whip instead. Sludge Bomb is a nice STAB coverage move that also gives it an advantage against other Grass-type picks.