This is the rulings section, which contains some information on game mechanics and abilites/items/moves. For simplicity sake, there will not be an explanation of Dynamaxing (as it is very straightforward and any Max moves will be mentioned as deemed most useful (either in the sets created in the comp sets section or later on this page). These basic rulings can affect your gameplay in a major way, so familiarize yourself with them; they will help.
Terrains are visible conditions which can be set up through the effects of dynamax moves (i.e. Max Lightning, Max Mindstorm, Max Overgrowth, Max Starfall), abilities (Grassy Surge, Psychic Surge, Electric Surge, Misty Surge), and terrain moves which set up the condition. Only one terrain can be on the field at a time, and they disappear only after 5 turns or if another terrain replaces it. If you feel a terrain will be an issue for your team, it would be best to have a terrain setter on your team to replace the terrain, or a pokémon which is designed to dynamax with one of the three max moves listed previously. They also have their own respective terrain seed items electric seed (+1 def), grassy seed (+1 def), misty seed (+1 sp.def), psychic seed (+1 sp.def) (one-time use items).
Electric Terrain boosts the power of electric moves by x1.5, and grounded pokémon cannot fall asleep. Any pokémon which were already asleep will not wake up when it becomes active, it will just prevent any other pokémon from falling asleep. This terrain is best used to accompany a teammate with great electric offense, with moves like Volt Switch and Thunderbolt, so that it can do more than just disrupt the opponent.
This terrain the boosts the power of grass moves by x1.5 and heals 1/16 of the health of grounded pokémon. It is one of the most common terrains in the metagame and benefits sweepers that use life orbs by restoring some of the health lost when they move. And so, this terrain is best paired with pokémon that lose health in order to fucntion. These strategies include Flame Orb Guts Sets (which also takes away 1/16 of your health each turn allowing the pokémon's health to remain neutral), Life Orb offensive sets, recoil-heavy offense mons, and stall pokémon which aim to last as long as possible.
This terrain boosts the power of psychic moves by x1.5 and prevents the use of priority moves onto grounded pokémon. It allows for glass cannons like Kartana, Alakazam and Dragapult to go on the offensive without worrying about a priority move like Sucker Punch, Extreme Speed, Aqua Jet or Shadow Sneak which would otherwise be able to one-shot them. Aside from the Grassy Terrain, this is another terrain which is used frequently, and so if your team has a hard time getting over certain pokémon which benefit from Psychic Terrain then it is advised that you have some way to prevent it from lasting, prefereably something that you can change somewhat easily.
On this terrain, dragon moves do x0.50 damage and grounded pokémon cannot be affected by status conditions. This terrain is best for disrupting any sort of strategies that revolve around using status conditions, such as Guts ability users, or pokémon that commonly use status moves like Toxapex and Ferrothorn. This means that any pokémon with dragon moves on your team will lose some power, so unless your pokémon have more than just all dragon moves that they would not be a good fit for your team.
Only one weather condition can be on the field at a time, and based on the weather certain effects take place. They typically last for 5 turns, but with items can be extended for up to 9 turns at a time.
In this condition, water-type moves do x1.5 more damage. It also reduces the power of fire-type moves by half. It can be extended with a Damp Rock, and is a suggested item to be held when settting up rain by pokémon such as Pelipper. The condition can be set up as the effect of Max Geyser, the Drizzle ability, or the move Rain Dance. Other moves to run in a rain-based team are moves such as Thunder and Hurricane, which will not miss in rain.
Note: This list does not mention the abilities that work in this condition, as those will be mentioned in sets regarding the weather
In this condition, fire-type moves do x1.5 more damage and water-type moves do half as much. It can be extended with the Heat Rock, and set into action as the result of Max Flare, the Drought ability, or the move Sunny Day. Some specific moves which work well in this weather condition are Solar Beam and Solar Blade, which will no longer need to wait a turn before being able to be used. There are a number of moves and conditions that recieve boosts/take affect from this weather condition, listed below:
Note: This list does not mention the abilities that work in this condition, as those will be mentioned in sets regarding the weather
In this condition, any pokémon that are not ground, rock, or steel type will lose 1/16th health each turn (assuming they don't have an ability or item which states otherwise). It also boosts the special defense stat of rock-type pokémon x1.5 and can be extended by a Smooth Rock. It can be set up with the ability Sand Stream, the move Sandstorm, or Max Rockfall. Unfortunately, this condition doesn't help the power of moves like the previous two do, but one move that (currently) gets a boost in this condition is Shore Up (restore 2/3 HP instead of 1/2). However, it is still a useful condition, as it also acts as a decent counter to Sun weather teams. More specifically, moves such as Morning Sun, Synthesis, and Moonlight will restore less health in sandstorm than sun (1/4th instead of 1/2 in normal conditions and 2/3 in Sun), and even the power of Solar Blade & Solar Beam do half as much damage.
In this condition, any non-ice type pokémon lose 1/16th HP each turn (assuming they don't have an ability or item which states otherwise). It can be extended with a Icy Rock and can be set up via the Snow Warning ability, effect of Max Hailstorm, or the move Hail. It provides the following effets:
Note: Out of all the weather conditions this is arguably the worst of the four to set up, and is evidently less popular as opposed to the other three.