Grass Monotype: In-depth analysis about aspects and matchups

Steel

Steel teams are very inconvenient to face for Grass thanks to their ability to freely switch in in a wide variety of situations and strike back really hard. Heatran, Skarmory, and Mega Scizor are the main threats, but they aren't really impossible to deal with. It is heavily recommended to have Fire and Ground coverage on Mega Venusaur, Cradily, or Celebi so this matchup gets easier.

Wincons: Mega Venusaur, Breloom

Other useful Pokémon: Ferrothorn, Celebi

Tips

1. Mega Venusaur is your first answer to Mega Scizor, thanks to its great bulk and ability to dish out lots of damage to it with Hidden Power Fire. However, it should be kept healthy for the most part of the game; don't make risky plays with it, or you most likely will have zero answers to Scizor.
2. If you anticipate Scizor setting up Swords Dance against your Ferrothorn or Cradily, don't be afraid to switch to Whimsicott and Encore it, as that can avoid your team getting swept or losing momentum with Mega Venusaur.
3. Heatran can be very challenging to handle, especially if it is holding an Air Balloon. If you are having trouble, a nice play is switching to Cradily and trying to break its Balloon with Rock Slide or then setting Stealth Rock. With its high special bulk, Cradily is able to take a few hits, and it can occasionally force Heatran out if it lacks Toxic. If you have Earthquake on Cradily or Mega Venusaur, however, this matchup shouldn't be a problem for you.
4. The match often starts with Skarmory setting up hazards, due to the ubiquity of hyper offense variants of Steel teams. It is recommended to take down Skarmory as soon as possible, so starting the battle with something that has Hidden Power Fire is a good choice.

Fire

This matchup is obviously tough, not only due to the type effectiveness, but also due to the sheer offensive pressure Fire teams are able to put on Grass, breaking through its core with ease. Cradily is pretty much a required Pokémon for this matchup, thanks to its ability to set Stealth Rock quite effectively as well as check important Pokémon on Fire teams.

Wincons: Cradily, Mega Venusaur, Shiftry

Tips

1. Make sure to keep Cradily healthy throughout the game. This is very important, because it is your most important check for lots of special attackers on Fire teams, most notably Mega Charizard Y.
2. As stated before, setting Stealth Rock and ensuring it stays up for the rest of the match can make this matchup a lot easier. Additionally, taking out Torkoal and/or the team's Defogger allows you to pressure the opposing team more reliably, making it less troublesome for your team to handle threats, as well as lowering opposing Pokémon's health to KO range to the point revenge killers like Serperior and Breloom can KO them.
3. Focus Sash Breloom is a nice lead for this matchup, considering Fire teams tend to start with their Infernape as a way of setting their hazards and preventing Cradily from doing anything. Rock Tomb deals solid amounts of damage to most Fire Pokémon, and it lowers Speed, punishing faster switch-ins.
4. Rock Slide Shiftry is a good way of checking Fire teams once Charizard Mega Evolves, thanks to Drought setting up sun and boosting Shiftry's Speed to high levels via Chlorophyll.

Poison

Poison is probably the least difficult disadvantageous matchup to handle for Grass, but it is still tough and annoying. It has got some nice tools to take down most Pokémon, ranging from Life Orb Nidoking to walls like Mega Venusaur and Weezing, which are very difficult to break without Psychic moves. If you have Celebi, however, this matchup isn't that much trouble.

Wincons: Celebi, Mega Venusaur

Other useful Pokémon: Cradily, Ferrothorn, Whimsicott

Tips

1. If you have Celebi, use its Psychic STAB move to deal lots of damage to common Poison threats. Thanks to its base 100 Speed stat, it can outspeed most Pokémon of the type. Watch out for Drapion and Skuntank, which are common switch-ins for Celebi due to their secondary Dark typing, so clicking Earth Power can be a good way to handle them.
2. Ferrothorn and Cradily are good ways of checking Gengar, especially when both are using a specially defensive spread, allowing them to switch into common moves like Sludge Wave and Shadow Ball and strike back with their STAB moves. Watch out for Focus Blast, though.
3. If you are having trouble handling opposing Mega Venusaur, PP stalling with Cradily is a good option to weaken it.

Flying

Flying teams usually rely on their great defensive core (Skarmory + Zapdos) to stop Grass teams in their tracks. This can get even worse if the opponent is using Charizard as their Mega option, thanks to its great wallbreaking power. Just like in Fire matchups, keeping hazards up is essential to victory.

Wincons: Cradily, Rotom-C

Other useful Pokémon: Mega Venusaur, Ferrothorn, Whimsicott

Tips

1. Volt Switch Rotom-C can be very useful for this matchup, since it handles Skarmory very well and can aid your team in keeping momentum.
2. It is advisable to keep Ferrothorn and Cradily healthy throughout the game, especially if the opposing team has Togekiss. These are able to take Air Slashes effectively from Scarf variants. Don't let your guard down, though; Togekiss usually runs Trick, and this can cripple these Pokémon for the rest of the game.
3. Whimsicott can do a great job by stopping common setup sweepers in their tracks, most notably Mega Gyarados. Also, don't hesitate to use Stun Spore against dangerous threats like Mega Charizard Y, Togekiss, Tornadus, and so on.

Psychic

Psychic is probably the hardest matchup for Grass teams. It is very difficult to break through Psychic's defensive core, especially Mew, with its ability to wall nearly every Grass-type pokemon. Furthermore, Psychic has a great offensive core that can easily break through nearly all Grass Pokémon, consisting of Victini, Mega Medicham, and Hoopa-U. You will have to take advantage of your opponent's mistakes and hope they aren't using specific sets that can be very troublesome for your team. If you have Shiftry, you might have an easier time handling the opposing team and be able to pull of a sweep should your opponent be caught off guard with Swords Dance or Substitute.

Wincons: Shiftry

Other useful Pokémon: Ferrothorn, Gourgeist-XL, Whimsicott

Tips

1. Keeping hazards up can help in wearing down Victini, which is a major threat for Grass teams.
2. If Mew has Taunt, paralyzing it with Stun Spore Whimsicott might be a good idea, allowing slower teammates like Cradily to use status moves, most notably Stealth Rock, before getting Taunted.
3. Status absorbers can work well against Mew (Celebi and Trevenant), since they don't mind Will-O-Wisp a lot and can usually stay in the field for a long period of time.
4. Preserving Ferrothorn can be very useful throughout the game, especially if the opposing team has Jirachi.

Bug

Grass vs Bug is a very annoying matchup, and it is somewhat hard to handle due to the great offensive pressure their Mega Pokémon, either Mega Heracross or Mega Pinsir, can put, as well as them having really good tools to get rid of your hazards (Armaldo and Forretress are both hard to take down outright), which should be one of your main ways to win the game. If you have Gourgeist-XL, then things might be way easier, since it can act as a reliable spinblocker in this matchup.

Wincons: Cradily, Mega Venusaur

Other useful Pokémon: Whimsicott, Ferrothorn, Gourgeist-XL

Tips

1. Aim to take down the opposing team's hazard remover (either Armaldo of Forretress, depending on the team). This will make it easier to set and keep up Stealth Rock, making the matchup dramatically easier.
2. Cradily is important for checking Volcarona. It has a good chance to survive most of it attacks, even after a boost, and it can strike back with Rock Slide, taking down offensive variants.
3. Mega Venusaur should be kept alive for Heracross and Scizor. Defensive sets can check Choice Scarf Heracross and prevent it from getting boosts via Moxie, as well as taking most Scizor attacks and striking it back with Hidden Power Fire.
4. Use Whimsicott to prevent important setup sweepers on the opposing side from using their boosting moves. Pinsir and Scizor are good examples of those, and it can be worth sometimes to switch into these Pokémon and use Encore if they used said moves.