Grass-type Pokémon are some of the most common in the games and the anime. Unlike most Water-types, Grass-types, along with Bugs, can be found early in the games, mainly in the first routes and the obligatory forest areas. It's also a fairly common type for Gym Leaders, with five of the eight regions having a Grass-type gym and Alola having a Trial Captain.
Grass is a complicated type to use, though. It has five 2x weaknesses, tying with Rock for the most weaknesses out of all types. It's also resisted by seven types, although it's strong against the Rock, Ground, and Water. Grass-types often depend on a secondary type to elevate their profile and make them more of a threat in battle. When used properly, Grass-type Pokémon can be quite effective, becoming invaluable assets in any team.
Shiinotic
The Fairy-type is absurdly overpowered, so any Pokémon that has it, even as a secondary type, will receive a considerable boost. Introduced in Generation VII, Shiinotic's stats may be unimpressive at first glance, but that doesn't mean it's a bad Pokémon. Sure, it has below average HP and Attack, and its Speed is pitiful. It has decent Sp. Atk and Sp. Def, which makes it a rather interesting choice.
Its secondary Fairy-typing means it gains a weakness to Steel and is now quad weak to Poison. However, it also loses its weakness to Bug, becomes immune to Dragon, and gains resistance to Fighting and Dark. Overall, Shiinotic may not be the best Pokémon, but it's certainly the best representative of its typing.
Vileplume
One of Generation I's strongest Grass-types, Vileplume is the final evolution of Oddish. Starting with a Base Stat Total of 480, Vileplume received a ten-point boost in its Special Attack during Generation VI, taking it all the way to 490. Its impressive 110 Sp. Atk is definitely its strongest asset.
Being a dual-type Grass/Poison Pokémon means that it not only loses its weaknesses to Poison and Bug, but it also gains resistance to Fighting and Fairy-types. It loses its resistance to Ground and gains a weakness to Psychic, but the pros outweigh the cons with this type-matchup, making Vileplume one of the best Grass-types in Gen I.
Decidueye
Starter Pokémon are usually some of the overall best in any given region, thanks to their high and balanced stats. Generation VII's Decidueye is no exception. A dual-type Grass/Ghost Pokémon, it boasts an exceptional 530 Base Stat Total, with particularly high Atk, Sp. Atk, and Sp. Def.
Its secondary Ghost typing means it loses weaknesses to Poison and Bug and gains immunities to Normal and Fighting. It also gains weaknesses to Ghost and Dark, though, and doesn't acquire any new resistances. Nevertheless, its strong move pool and status as a Starter make Decidueye one of the most reliable, and best-designed, Grass-types.
Ludicolo
One of the most memorable Pokémon from Generation III, Ludicolo is truly unique. It has an average stat of 480, which might not seem like much at first. It's mainly a Special Attacker with average HP, Speed, Defense, and Attack.
Ludicolo, however, is a Water/Grass Pokémon, something that immediately makes him a threat. Its primary Water-typing means it loses weaknesses to Fire and Ice and becomes resistant to the powerful Steel-type. It also means that it loses its resistance to Grass and Electric, though. Ludicolo is still a worthy choice for any team, not to mention it's an incredibly fun Pokémon.
Cradily
Fossil Pokémon can be pretty hit-or-miss, especially because of their obligatory Rock-typing. Cradily's unique combination of Rock and Grass, however, actually works in its favor. Despite being the two types with the most weaknesses, they balance each other out and end up with only four.
Rock loses its weakness to Grass, Ground, and Water, while Grass loses its own weaknesses to Fire, Bug, and Poison. Cradily is also resistant to Normal and Electric, which is a nice addition. Its Base Stat Total is a respectable 495, but if it's a good enough Pokémon for a Champion like Steven, then it's good enough for the average Pokémon team.
Roserade
One of Generation IV's best Grass-types, Roserade was introduced as an evolution to the Gen III Pokémon Roselia. Starting with a Base Stat Total of 505, it too received a 10 point boost in Gen VI, increasing its defense to a still bad 65, but taking its overall total to 515.
A strong Special Attacker, Roserade is a staple in most Sinnoh teams. Even the region's Champion, Cynthia, has one. Like Vileplume, Roserade's typing means it loses weaknesses to Bug and Poison and gains resistances to Fighting and Fairy. In return, it gains a weakness to Psychic and loses its resistance to Ground. A fair exchange, overall.
Venusaur
Kanto Starters will always have a special place in any Pokémon fan's heart. They are three of the most popular and recognizable Pokémons, after all. And while Venusaur and Blastoise don't receive nearly half the exposure that Charizard does, they're still important figures within the Pokémon universe.
A dual-type Grass/Poison mon, Venusaur has very balanced stats, with both Special attributes as its biggest assets. Venusaur received a Mega Evolution in Gen VI, taking its Stat Total to a massive 625. In Gen VIII, it also received a Gigantamax form, confirming its place as one of the franchise's most important creatures.
Torterra
Generation VI's Grass-type Starter, Torterra features a clever and instantly attractive design. Like other Starters, it has a 525 Base Stat Total, with Attack and Defense as its highest attributes.
Torterra also has a unique type combination, making it even more special. Its secondary Ground-type means it loses its weakness to Bug and gains immunity to Electric. It also means, however, that it loses its resistance to Grass, and becomes four-times weak to Ice. Still, Torterra is a strong, imposing Pokémon that will be a great companion for any Sinnoh playthrough.
Ferrothorn
Steel is, without a doubt, the best type in the games. It resists ten types, is super effective against three, including the overpowered Fairy, and weak to only three more. Four types resist Steel-type attacks, but most are also weak to Ground attacks, which Steel-types can easily learn.
Ferrothorn's dual Grass/Steel typing means it loses nearly all its weaknesses. It actually becomes immune to Poison, while gaining resistances to Normal, Rock, Steel, Psychic, Dragon, and Fairy. And while it gains a weakness to Fighting and becomes quad weak to Fire, the gains absurdly outweigh the losses, making Ferrothorn an ideal choice for any Pokémon team.
Kartana
Ultra Beasts exist in a strange place within the Pokémon universe. Some fans consider them Legendaries, while others don't. They're exclusive to the Alola region, which makes them rather niche, and their designs are divisive, to say the least. However, there's no denying they're super strong.
Kartana, like Ferrothorn, is a Grass/Steel type, meaning it's absurdly powerful. With a super high 570 Base Stat Total, only two weaknesses, one immunity, and resistances to nine different types, Kartana is an extremely powerful Pokémon that definitely elevates the Grass-type's average as a whole.