Grookey, the grass starter in Pokémon Sword and Shield, has three main evolutions: Grookey, Thwacky and Rillaboom. Once it becomes a Rillaboom, it can also access its Gigantamax form by visiting the Isle of Armor. Not to worry — evolving the funky spider monkey into the drummer of the jungle is easier than keeping a beat.
All of Grookey’s forms will have Overgrow, which makes grass-type moves stronger when its HP is 1/3 or less. It can also learn the hidden ability Grassy Surge, which creates Grassy Terrain when the Pokémon enters the field. As a grass-type Pokémon throughout its three evolutions, it is weak to fire, bug, poison, ice, and flying-type moves, but it takes less damage from water, grass, electric, and ground-type moves. This Pokémon will shine brightest when pitted up against Pokémon that are weak against grass-type moves — such as rock, ground and water-types. Taking advantage of these weaknesses, combined with its damage boost from both being a grass-type Pokémon and having an ability that boosts the damage output of grass-type moves, makes it a massive threat to these types.
Although categorized as the Chimp Pokémon (a category it shares with Chimchar, the fire starter from Pokémon Diamond and Pearl), Grookey’s resemblance is more akin to a spider monkey’s. Once it evolves, the chimp classification makes more sense. To obtain Grookey, choose it as a starter from Leon. The starter chosen has a chance of being either male or female, but don’t hold your breath for a female since the likelihood of receiving a female starter is only 12.5%.
If the player didn’t choose Grookey as their starter, the only way to obtain it would be to trade with other players or use Surprise Trade and hope to get lucky. From here, take Grookey into Pokémon battles to level it up. It levels up at the same speed as the other starters in the game, and with stats lower than that of its various evolutions, trainers should aim to evolve Grookey quickly. Once it hits level 16, it will evolve into Thwackey.
Thwackey, the Beat Pokémon, walks around on two legs and has more attitude than its prior evolution. Reaching this evolution gives the player the choice to teach Thwackey Double Hit, a normal-type move that hits the opponent twice. Since this is not a grass-type move, attacking a Pokémon with resistance to grass would be its only use.
Thwackey is a pure grass-type and therefore has the same strengths, weaknesses and resistances as Grookey. At this stage, keep leveling up until Thwackey reaches level 35, where it will become Rillaboom. Players can use rare candy as a shortcut to this level, but rare candy is much more beneficial at higher levels.
Finally, Rillaboom, the Drummer Pokémon, is ready to be unleashed. The spider monkey has finally become a full-grown gorilla, complete with a new drum that it carries on its back. At this stage, It will be able to learn its signature move, Drum Beating. Drum Beating allows Rillaboom to use its drum’s roots to attack the target and lower its speed stat.
Despite its increased size, stat boosts and gaining an excellent bass drum that it uses in battle, Rillaboom doesn’t change things much for the Pokémon. It still shares the same weaknesses, resistances and abilities as its previous evolutions, as is the case with all the Galar region starters. Rillaboom is the final evolution for the grass starter, but it isn’t its final form.
Along with adding a new adventure and legendary Pokémon, Pokémon Sword and Shield‘s first expansion, The Isle of Armor, introduced the ability to Gigantamax Galarian starter Pokémon. However, Rillaboom cannot be Gigantamaxed right away. The player first has to complete trials for Dojo Master Mustard, which appear organically while playing through the DLC’s main story. After the second trial, Mustard will request three Max Mushrooms, the main ingredient in Max Soup. These mushrooms are scattered throughout the island and appear at the base of large pinkish-red mushrooms.
After collecting the mushrooms, bring them back to the Dojo’s kitchen to be taught how to make Max Soup. Max Soup is an item that gives any Pokémon with Gigantamax potential access to their Gigantamax form and their G-max move in battle. Present this soup to Rillaboom, and it will gain the ability to become Gigantamax Rillaboom when in a Pokémon battle that allows Dynamaxing.
Gigantamax Rillaboom has exclusive access to the G-max Drum Solo. This powerful grass-type attack ignores any effects of the target’s ability, as long as Rillaboom knows a grass-type attack as one of its four moves. Its power is 160 regardless of the base move it is equipped with and will do special or physical damage depending on the type of damage its base move inflicts. Such an attack is practical when up against Pokémon with abilities that allow them to avoid damage from Rillaboom’s base attack and can be devastating to an opposing Pokémon that is weak against grass-type moves.