Weather

Weather is an important aspect of dungeons and should always be taken into account as it impacts gameplay and dungeon difficulty. Ιt also affects the aesthetics of the overworld.

Weather occurs naturally in most dungeons or is triggered by enemy Pokémon's Abilities. Obviously, most enemy Pokémon in a dungeon are adapted to the local weather and benefit drastically from it. For example, Pokémon with Sand Veil are usually present in Sandstorm. However, the player can break this synergy by taking advantage of the local weather or by changing the weather to their own advantage. In general, creating weather-based synergy within the team or party can significantly boost chances of survival in tough dungeons and reduce conflict "weather fights". Players can change the weather themselves through moves, Abilities and weather rocks. A weather condition lasts until entering the next floor or until someone else changes the weather (e.g. a Drizzle Pokémon spawning or a Cherrim using Sunny Day). Weather moves can be used any time, but weather Abilities require the Pokémon to enter the floor to be triggered. Weather rocks are items that need to be held by a team member to give a weather condition effects to the player only, provided that the external weather is Clear (except for the Clear Rock that overwrites other weather conditions). Weather rocks can be purchased from the Dark Market in Tanren Undercity, and found in certain dungeons. In PMU, weather is also crucial because it activates Gems and Crystals. These are bag items that give significant buffs to your team's Pokémon of the same type, by granting immunity to status problems and by giving Speed Boost to that type respectively. Since PMU is a real-time, rather than turn-based, game and status problems are very common, Gems make a great deal in planning out a strategy. PMU 7 features the weather conditions encountered in PMD and the core series. There are a total of 9 different weather conditions (10 if Clear weather is considered), each with different gimmicks. Most conditions buff or nerf a particular Pokémon type, but also have general effects that affect all types. In this sense, some family items activate only during particular weather conditions.

It's important to note that, moves that become 100% accurate in certain weather only take in account what condition the enemy Pokémon is in. For example, holding an Icy Rock in Clear weather will not make Blizzard's accuracy 100%. This means, however, if it were Hailing while holding a Clear Rock, Blizzard will be 100% accurate.

Clear
Clear weather is the standard weather and has no particular effects. It is crucial for the activation of weather rocks.
 * Cannot be triggered by moves
 * Triggered by the Ability Cloud Nine (Golduck, Lickilicky and Altaria lines)
 * Triggered by the Clear Rock when held by a team member. Does not stack with other weather rocks
 * Typically used in conjunction with weather rocks
 * Activates the Fight, Sky, Guard (Bug), and Dragon Gems and Crystals

Cloudy
This is considered the weather for Normal-types. It essentially nerfs all types but Normal, but its effects are not that devastating or even noticeable.
 * Cannot be triggered by moves or Abilities
 * Triggered by the Cloudy Rock in Clear weather
 * Reduces damage by non-Normal-type moves by 25%
 * Reduces HP regain by Morning Sun, Moonlight and Synthesis
 * Activates some family items for Normal-types
 * Activates the White (Normal), Poison, and Thunder Gems and Crystals

Rain
The weather that buffs Water-type and nerfs Fire-type.
 * Triggered by the move Rain Dance
 * Triggered by the ability Drizzle (Politoed, Pelipper, Kyogre)
 * Triggered by the Damp Rock when held by a party member in Clear weather
 * Doubles damage by Water-type moves
 * Halves damage by Fire-type moves
 * Raises the accuracy of the moves Thunder and Hurricane to 100%
 * Reduces HP regain by Morning Sun, Moonlight and Synthesis
 * Longer recharge time for Solar Beam
 * Makes the floor damp (prevents explosions by items, traps, moves or Abilities)
 * Activates the Abilities Swift Swim, Hydration, Dry Skin, Rain Dish, Forecast
 * Activates family items that require Rain
 * Activates the Aqua Gem and Crystal

Sunny
Opposite to the Rain, this weather buffs Fire-type and nerfs Water-type. Additionally buffs Grass-type and Fairy-types, creating good synergy between the three types.
 * Triggered by the move Sunny Day
 * Triggered by the Ability Drought (Ninetales line, Torkoal, Groudon)
 * Triggered by the Heat Rock when held by a party member in Clear weather
 * Doubles damage by Fire-type moves
 * Halves damage by Water-type moves
 * Cuts the accuracy of the moves Thunder and Hurricane to 50%
 * Raises HP regain by Morning Sun, Moonlight and Synthesis
 * No recharge time for the move Solar Beam
 * The move Growth raises Attack and Special Attack by two levels
 * Pokémon cannot be frozen
 * Activates the Abilities Chlorophyll, Dry Skin, Flower Gift, Leaf Guard, Solar Power, Forecast, while buffing Harvest
 * Activates family items that require Sun.
 * Activates the Fiery, Grass, and Pixie Gems and Crystals

Diamond Dust
PMU's unique weather, Diamond Dust is the second condition to buff Fairy-types.
 * Cannot be triggered by moves or Abilities
 * Triggered by the Sparkle Rock in Clear weather
 * Fairies get Speed Boost (double movement speed)
 * Player evasion raises by one level
 * NPC evasion drops by one level

Snow
Like Fairy-types, Ice-types are also favored by two weather conditions, in fact exclusively. Snow works similarly to Diamond Dust, but for Ice-types.
 * Cannot be triggered by moves or Abilities
 * Triggered by the Snowy Rock in Clear weather
 * Ice-types get Speed Boost (double movement speed)
 * Reduces HP regain by Morning Sun, Moonlight and Synthesis

Hail
Hail is the second condition that favors Ice-types, while nerfing all other types.
 * Triggered by the move Hail
 * Triggered by the Ability Snow Warning (Abomasnow, Amaura and Alolan Vulpix lines, Vanilluxe)
 * Triggered by the Icy Rock when held by a party member in Clear weather
 * All types but Ice cannot regain HP naturally by walking and instead lose HP. Pokémon with the Abilities Snow Cloak, Slush Rush, Ice Body, Overcoat, and Magic Guard are immune to this effect
 * Raises the accuracy of the move Blizzard to 100%
 * Reduces HP regain by Morning Sun, Moonlight and Synthesis
 * Activates the Abilities Snow Cloak, Slush Rush, Ice Body, Forecast
 * Activates the Icy Gem and Crystal

Sandstorm
Sandstorm works similarly to Hail but for the earth types. This weather buffs Rock-, Ground-, and Steel-types, thus creating good synergy between them, while nerfing all other types. It also harms the player's vision, as it makes it very difficult to navigate through the map without Safety Goggles or Sandstorm Specs.
 * Triggered by the move Sandstorm
 * Triggered by the Ability Sand Stream (Hippopotas line, Tyranitar, Gigalith)
 * Triggered by the Smooth Rock when held by a party member in Clear weather
 * All types but Rock, Ground and Steel cannot regain HP naturally by walking and instead lose HP. Pokémon with the Abilities Sand Rush, Sand Veil, Sand Force, Overcoat, and Magic Guard are immune to this effect
 * Raises the Special Defense of Rock-types by 33%
 * Reduces HP regain by Morning Sun, Moonlight and Synthesis
 * Reduces visibility without Safety Goggles or Sandstorm Specs.
 * Activates the Abilities Sand Rush, Sand Veil, Sand Force
 * Activates the Stone, Earth, and Metal Gems and Crystals

Fog
The fog is the weather condition that buffs the mystical types Psychic, Ghost and Dark, while nerfing Electric-types. It also harms the player's vision, as it makes it very difficult to navigate through the map without Safety Goggles.
 * Cannot be triggered by moves or abilities
 * Triggered by the Foggy Rock in Clear weather
 * Halves the damage by Electric-type moves
 * Reduces HP regain by Morning Sun, Moonlight and Synthesis
 * Reduces visibility without Safety Goggles
 * Activates the Psyche, Shadow, and Dark Gems and Crystals

Ashfall
Ash is a unique weather condition only in Ash Forest. It buffs the Poison-type while nerfing Electric-types.
 * Cannot be triggered by moves or Abilities
 * Increases damage by Poison-type moves
 * Halves damage by Electric-type moves

Trivia

 * While Diamond Dust weather is not present in the Pokémon Mystery Dungeon series' games, it is an actual weather effect in some of the main series' games.