In Pokemon Sword and Shield the starters are really inviting and - like any self-respecting Pokemon game - it's always difficult to have to choose.
In Pokemon Sword and Shield the first starter Pokemon is Grookey, an adorable greenish grass-type monkey. Like any creature of that type, he is weak to fire, beetle, poison, steering wheel and ice, while being super effective against rock, earth and water types.
At level 16, Grookey evolves into Thwackey, an upright monkey holding a stick slightly larger than the one held by its pre-evolution. He too remains a grass-type Pokemon. Finally, at level 35 it evolves into Rillaboom, a huge primate that looks like it's kicking a drum kit. Like all other Pokemon of its kind, too Rillaboom remains grass type.
The passive ability of Grookey it is Herb Help, which boosts Herb moves by 50% (excluding STAB) when the Pokemon has a third or fewer health points of its total. Example: if Thwackey has 60 HP, the ability activates from 20 HP up to 1 HP. Through a special event, it will be possible to obtain and breed a Grookey with the Herbogenesis ability, which creates a Grassy Field at the entrance to the Pokemon's ground, and confers various advantages, including the constant HP recovery and the 50% increase in the power of Grass-type moves (excluding STAB ).
The exclusive move of Rillaboom it is Drum Attack, an 80-power physical move that reduces the opponent's speed as a side effect. It is learned through evolution, at whatever level you decide to evolve Thwackey.
You will get Grookey only by choosing it as your starter Pokemon. If not, you will have to try your luck in the Magic Exchange or find some friends willing to exchange it.
Have you seen the evolution lines of Scorbunny and Sobble instead?