Rillaboom

Rillaboom has a lot of raw potential, and could very well end up the apex of the Grass Type starters down the road. It has high raw power, and really only lacks access to Frenzy Plant to make its mark. It's not quite up to par with the royalty of the type, but it's still great.

Max Battles

Rillaboom possesses the highest overall stats amongst all starter Pokemon. It has ~20% more Attack than Venusaur and roughly equal bulk. It is currently slightly outclassed by Gigantamax Venusaur due to the sheer power of G-Max moves, but Rillaboom has its own Gigantamax form in the future to take the crown back. Either way, you may not want to get too attached in investing too much into Rillaboom right now.

For players who cannot get their hands of a Gigantamax Venusaur, Rillaboom's Max Overgrowth is still very powerful. One of Rillaboom's flaws is that Razor Leaf is not a 0.5 second duration move, so it does not charge the Max Meter quickly. Therefore, it is preferable to pair Rillaboom with another Pokemon with a 0.5s move such as Vine Whip Venusaur. They can help charge the meter more quickly, and then they can switch to Rillaboom for a stronger Max Overgrowth.

Best PvE Offensive Moveset

• Razor Leaf pairs with Grass Knot for the best Grass Type damage that Rillaboom can muster until it gains access to Frenzy Plant.
• Scratch, Energy Ball, and Earth Power all fall behind in traditional DPS sense. However, as Scratch is a 0.5s move, it is useful in higher tier Max Battles to charge the Max Meter more quickly. Keep in mind that it will result in Max Strike instead of Max Overgrowth during the Dynamax phase.

Best PvE Defensive Moveset

• Razor Leaf sports good Defensive performance, while Earth Power grants counter-coverage against most Fire Types.
• Scratch, Grass Knot, and Energy Ball all fall behind.

Razor Leaf is primarily damage-oriented and has low energy gains, but it's superior to the competition. Grass Knot provides the lowest cost move at Rillaboom's disposal, while Earth Power provides reasonable coverage.