Dynamax Rillaboom

Dynamax Rillaboom is a real bruiser of a Dynamax Pokemon, capable of causing a lot of damage with its Max Overgrowth while supporting decent bulk. However, it lacks a Grass Type 0.5 second Fast Move, so it doesn't generate energy extremely well. On defense it can rely on Scratch for this job, but there are objectively better options for this role. Having a 1 second Fast Move isn't the worst fate for an offensive Dynamax Pokemon, as players tend to switch them in to drop Max Moves and then back out to keep them safe, but it can still have moments where it's a bit on the slow side.

Honestly, Dynamax Rillaboom is heavily overshadowed by its Gigantamax forme, which can rely on Scratch and still belt out a G-Max Drum Solo, which is literally Max Overgrowth, but better. This is a solid starting point, but you're probably better off saving your resources for the Gigantamax version.