Venusaur

Venusaur was once the top Grass Type attacker. This isn't thanks to its stats, but rather its moveset. As the first Pokemon to not only get Frenzy Plant but any of the starter moves, Venusaur is still viable, but it's fallen from grace greatly. Still, it's worth raising at least one for Mega Venusaur.

Max Battles

As far as Dynamax Venusaur goes, it's a good Grass Type with solid performance, but it's a bit behind Rilaboom when it comes to Max Move damage output, and it's already outclassed by its own Gigantamax forme maybe don't invest too much in this one.

Defensively, Venusaur has seen better days. Grass is resisted by 7 types and Venusaur suffers weaknesses to a few key offensive types that are still running rampant in 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 Venusaur.
• Return has no use on an offensive 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 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 due to being a 1-bar move.
• Solar Beam is too slow for defense. 
• Return is a 3-bar move that's hard to dodge and has good neutral coverage, though it is a bit weak.

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.