Castform Weather
Everyday there will be a different Castform Icon on the right side of the userbar. Each Castform icon represents the weather on the game, and for each specific weather, a specific type of Pokemon will gain 50% more EXP. This does not affect eggs.
If you hover over the Castform Icon on-game, it will say what Pokemon type will gain 50% more EXP.
Castform Weather Icons
Clear Sky - There is not even one cloud in the sky. (All Normal Pokémon gain 50% more EXP.)
Rainy - Better take an umbrella. (All Water Pokémon gain 50% more EXP.)
Cold - That's cold! (All Steel Pokémon gain 50% more EXP.)
Hail - Watch out for hailstones! (All Ice Pokémon gain 50% more EXP.)
Strong earthquakes - WARNING: There will be powerful earthquakes from time to time. Better stay at home! (All Ground Pokémon gain 50% more EXP.)
Very Sunny - Don't stay too long in the sun! (All Fire Pokémon gain 50% more EXP.)
Meteorites - Special warning: Watch out for meteorites falling from the sky. (All dragon Pokémon gain 50% more EXP.)
Gusty - That's gusty! I might get blown away! (All Fighting Pokémon gain 50% more EXP.)
Mystic Aurora - ... What's that? That aurora looks amazing! (All Psychic Pokémon gain 50% more EXP.)
Thunderstorm - Wow, lightning! (All Electric Pokémon gain 50% more EXP.)
Windy - It blows a pleasant breeze. (All Flying Pokémon gain 50% more EXP.)
Sunny - Oh, I like sun! Just like my plants do. (All Grass Pokémon gain 50% more EXP.)
Small earthquakes - During the day it will come to weak earthquakes. (All Rock Pokémon gain 50% more EXP.)
Muggy - Man, it's muggy today. (All Bug Pokémon gain 50% more EXP.)
Very foggy - I can no longer see my hands in front of my face! (All Dark Pokémon gain 50% more EXP.)
Smog - A large cloud of smog moves from the big city here. (All Poison Pokémon gain 50% more EXP.)
Foggy - The fog is blocking my view... (All Ghost Pokémon gain 50% more EXP.)