Things work a bit differently in the Pokemon TCG compared to the games or anime. There are 18 types of Pokemon overall but these get compressed into 11 types for the TCG. This means that some TCG types are combinations of multiple groups. Grass-type includes almost all Grass and Bug Pokemon as well as quite a few Poison Pokemon from Generation One up until Generation Three.
Grass Pokemon are some of the most versatile in the series. They can deal out many types of special conditions, recover HP, and stall foes into submission. However, trying to do everything in one deck will leave a player without resources very quickly with many half-implemented strategies. Focusing on a few specific strengths is a better approach for success.
Call For Backup
The Active Pokemon may be the one doing the battling but those on the Bench are equally important. If a trainer ever runs out of Pokemon on their side, they automatically lose. Many Grass-types have the ability to call for reinforcements with low-energy moves. This is a great way to set up basic Pokemon, or greater, quickly and efficiently.
A few in the Sword & Shield expansion have this ability, like Celebi V. A few more Pokemon in the player's hand or Bench also gives them a bit of security in case the opponent has a trick up their sleeve. A great opening gambit, regardless of deck strategy.
Poison Foes
Poisoned is a special condition that applies 10 damage to an afflicted Pokemon each turn. Many Grass-types in the TCG, like Beedrill from the Champion's Path expansion, can apply this status ailment with very little cost and sometimes while doing decent damage.
Unlike other special conditions, Poisoned cannot go away passively. It stays with the afflicted Pokemon until it either faints or is healed. Over time, this can topple even the toughest foes.
Paralyze & Prey
Paralyzed is a special condition that renders a Pokemon unable to move or retreat for one turn. At their turn end, they lose this condition and return to normal. By itself, this effect simply locks a foe down for a turn, which can be very useful, though the best implementation of this ailment is to combine it with damage to widdle a foe's health away while preventing them from fighting back.
Since there's usually a coinflip required to determine if an attack paralyzes the target, this can be a gamble. Shuckle from the Rebel Clash expansion has the attack Bind, which is a prime example of this strategy.
Lull Enemies To Sleep
Asleep is another special condition that prevents the opponent from attacking or retreating, though it differs from Paralysis. At the end of a sleeping Pokemon's turn, their trainer flips a coin. If heads, the Pokemon awakens, and if tails, it stays asleep.
This is another excellent way to lock down a foe. While they are sleeping, the player can inflict damage upon them with near-impunity. Abomasnow, also from the Rebel Clash expansion, can even put foes to sleep while doing 80 damage with Soothing Scent. No coin flip required.
Confuse & Conquer
Confused is potentially the most adverse of all the special conditions if the afflicted is unlucky. When suffering from this status ailment, the Pokemon's trainer will have to flip a coin each time they wish to attack. If heads, the attack goes as planned, but if tails, their Pokemon takes 30 damage instead of performing their intended move.
This is another condition that does not go away by itself and can force a foe to hurt themselves on their own turn, combining insult and injury. Butterfree V from the Darkness Ablaze expansion turns foes on themselves easily with a low-cost Dizzying Poison, which also applies the Poisoned condition to them.
Assail Adversaries With Multiple Conditions
Certain status conditions afflict Pokemon in different ways. Being Paralyzed will force the card to be turned clockwise on the field, Asleep will turn it counter-clockwise, and Confused will set it upside down. These three cannot usually be active at the same time but Pokemon suffering from one of these can also be Poisoned, much like in Butterfree V's attack.
There are other butterfly-like Pokemon that have attacks like this as well. Vivillon from the Forbidden Light Expansion has Vivid Powder, an attack that makes the foe Poisoned and Asleep simultaneously while also doing 50 damage. Having a deck full of butterflies sounds cute but could be a deadly strategy.
Regrow & Ravage
Most of the time, healing is only possible through item card usage, though some Grass-type Pokemon possess the power to regenerate HP. Certain moves grant them health upon specific criteria being met or as the effect of an attack. Ludicolo from the Rebel Clash expansion has a Mega Drain attack that does a substantial 120 damage and also heals them for 30 HP.
There are even some Abilities that can do similar feats. This in combination with afflicting special conditions can put the opponent in a seemingly hopeless situation.
Energize One's Team
Attacks and Abilities that result in more energy getting attached to one's Active or Bench Pokemon can lead to a whole team being ready to attack at any moment. Spare energies can even be used as emergency retreat resources.
The Sword & Shield expansion has a Rillaboom card with such an Ability. This card's Voltage Beat lets their trainer pull two grass energy cards from their deck and attach them to any of their Pokemon. Getting more energies onto a team can mean that more powerful attacks are able to unleash quicker. This strategy works well with many others, acting as a quick way to fuel one's powerhouse cards.
Interrupt The Opponent's Strategy
Focusing on your own strategies is all well and good, but ignoring what the opponent is up to can be disastrous. They may have drawn a great starting hand and are close to unleashing their strongest weapon. Instead of suffering it, a trainer could throw a wrench into the enemy's plans by causing their Active Pokemon to lose energy, forcing them to discard their hand, or even wreaking havoc on their Bench Pokemon.
Whimsiscott from the Sword & Shield expansion can force the opposing Active Pokemon to be shuffled back into their deck along with all attached cards, essentially resetting the foe's plan.
Think About Venusaur To Be The Deck's Core
There have been many Venusaur cards released since the TCG was created in the late '90s. They all vary quite a lot in appearance and strength, though they have a consistent pattern. Venusaurs typically have Abilities and multiple moves that heal themselves, manipulate energy in some way, deal huge damage, or apply special conditions to the foe.
All of which offer great support and offensive traits that can synergize with many other Grass-type cards. Most grass decks can't go wrong with a couple of Venusaurs.