Weather

Weather is an important gameplay element prominent in dungeons that impacts gameplay and difficulty.

There are different kinds of weather conditions, each with its own kinds of effects associated with it such as modifying moves, stats, or triggering Abilities and more. Weather occurs naturally in dungeons or is triggered by certain Abilities, moves and items, lasting indefinitely on the dungeon floor unless the weather is changed through the aforementioned methods.

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 effect to the player only, provided that the external weather is clear (barring 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 crucial for Gems, Crystals and some family items to work. They are kinds items only needed to be kept in the bag that give status immunity and boosted movement speed respectively, with a family item's effect depending on the Pokémon.

Moves which have their accuracy altered in certain weather only take in account what condition the enemy Pokémon is in. For example, holding a Damp Rock in clear weather will not affect Hurricane's accuracy. This does mean, however, if it were raining while holding a Clear Rock, Hurricane will bypass accuracy.

List of Weather Conditions
PMU features weather conditions encountered in both PMD and the core series, as well as a couple conditions exclusive to it.

Clear
Clear weather is the standard weather and has no particular effects. It is crucial for the activation of weather rocks.
 * Triggered by:
 * The Ability Cloud Nine and Air Lock
 * A when held (does not stack with other weather rocks)
 * A
 * Activates:
 * Family items that require clear weather
 * Fight, Sky, Guard (Bug), and Dragon Gems and Crystals

Cloudy
Cloudy is considered the weather for Normal-types; it essentially nerfs all types but Normal. Cloudy weather via the weather rock does not include the damage reduction.
 * Triggered by:
 * A in clear weather
 * A
 * Affects moves:
 * Halves the damage of non-Normal-type moves
 * Weather Ball has its power doubled
 * Reduces HP regained by Morning Sun, Moonlight and Synthesis
 * Activates:
 * Family items that require cloudy weather
 * White (Normal), Poison, and Thunder Gems and Crystals

Rain
The weather that buffs Water-types and nerfs Fire-types.
 * Triggered by:
 * The move Rain Dance
 * The Ability Drizzle
 * A when held in clear weather
 * A
 * Affects moves:
 * Increases the damage of Water-type moves by 1.25x
 * Halves the damage of Fire-type moves and Solar Beam
 * Reduces HP regained by Morning Sun, Moonlight and Synthesis
 * Thunder will never miss
 * Hurricane has its accuracy increased
 * Weather Ball becomes Water-type and has its power doubled
 * Activates:
 * The Abilities Swift Swim, Hydration, Dry Skin, Rain Dish, Forecast
 * Family items that require rain
 * Aqua Gem and Crystal

Sunny
Opposite to rain, this weather buffs Fire-types and nerfs Water-types. Additionally buffs Grass-types and Fairy-types, creating good synergy between the three types.
 * Triggered by:
 * The move Sunny Day
 * The Ability Drought
 * A when held in clear weather
 * A
 * Affects moves:
 * Increases the damage of Fire-type moves by 1.25x
 * Halves the damage of Water-type moves
 * Halves the accuracy of Blizzard, Thunder and Hurricane
 * Weather Ball becomes Fire-type and has its power doubled
 * Increases HP regained by Morning Sun, Moonlight and Synthesis
 * No recharge time for the Solar Beam and Solar Blade
 * Growth raises Attack and Special Attack by two stages
 * Activates:
 * The Abilities Chlorophyll, Dry Skin, Flower Gift, Leaf Guard, Solar Power, Forecast
 * Family items that require sun.
 * Fiery, Grass, and Pixie Gems and Crystals
 * Prevents Pokémon from being

Hail
Hail favors Ice-types, while nerfing all other types.
 * Triggered by:
 * The move Hail
 * The Ability Snow Warning
 * An when held in clear weather
 * A
 * Affects moves:
 * Halves the damage of Solar Beam
 * Blizzard has its accuracy increased to 90%
 * Weather Ball becomes Ice-type and has its power doubled
 * Reduces HP regained by Morning Sun, Moonlight and Synthesis
 * Activates:
 * The Abilities Snow Cloak, Slush Rush, Ice Body, Forecast
 * Family items that require hail
 * Icy Gem and Crystal

Snow
Like Fairy-types, Ice-types are also favored by two weather conditions.
 * Triggered by:
 * A when held in clear weather
 * A
 * Affects moves:
 * Halves the damage of Solar Beam
 * Blizzard has its accuracy increased to 90%
 * Weather Ball becomes Ice-type and has its power doubled
 * Reduces HP regained by Morning Sun, Moonlight and Synthesis
 * The movement speed of Ice-types increases by one stage

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.
 * Triggered by:
 * The move Sandstorm
 * The Ability Sand Stream
 * A when held in clear weather
 * A
 * Affects moves:
 * Halves the damage of Solar Beam
 * Weather Ball becomes Rock-type and has its power doubled
 * Reduces HP regained by Morning Sun, Moonlight and Synthesis
 * Activates:
 * The Abilities Sand Rush, Sand Veil, Sand Force
 * Family items that require sandstorm
 * Stone, Earth, and Metal Gems and Crystals
 * All types but Rock, Ground and Steel take damage over time by walking. Pokémon with the Abilities Sand Rush, Sand Veil, Sand Force, Overcoat, and Magic Guard are immune to this effect
 * Boosts the Special Defense of Rock-types by 1.5x

Fog
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. Fog weather via the weather rock does not include the damage reduction.
 * Triggered by:
 * A when held in clear weather
 * A
 * Affects moves:
 * Halves the damage of Electric-type moves
 * Halves the damage of Solar Beam
 * Weather Ball has its power doubled
 * Reduces HP regained by Morning Sun, Moonlight and Synthesis
 * Activates:
 * Family items that require fog
 * Psyche, Shadow, and Dark Gems and Crystals

Diamond Dust
Diamond dust is the second condition to buff Fairy-types.
 * Triggered by:
 * A when held in clear weather
 * Affects moves:
 * Weather Ball has its power doubled
 * The movement speed of Fairy-types increases by one stage
 * Player evasion increases by one stage
 * NPC evasion lowers by one stage

Ashfall
Ashfall buffs the Poison-type while nerfing Electric-types. It is the only weather condition that does not have a rock variant.
 * Affects moves:
 * Increases the damage of Poison-type moves by 1.25x
 * Halves the damage of Electric-type moves
 * Halves the damage of Solar Beam
 * Weather Ball becomes Rock-type and has its power doubled
 * Reduces HP regained by Morning Sun, Moonlight and Synthesis

Trivia

 * While diamond dust and ashfall weather is not present in the Pokémon Mystery Dungeon series' games, they are actual effects in some of the main series' games.
 * Ashfall was first introduced in PMU 7 with the release of Ash Forest.