Ability
Forecast
Castform's type changes to the current weather condition's type, except Sandstorm.
Weather Sandstorm
Lasts 5 turns (8 with Smooth Rock). At the end of each turn, Pokémon that aren't Rock, Ground or Steel type lose 1/16 of their max HP (unless they have Abilities such as Sand Rush, Sand Veil, Sand Force, Overcoat or Magic Guard). Rock-type Pokémon get 1.5× Special Defense.
Pokémon with Forecast (1)
"hidden" means it is that form's hidden ability. Megas have a fixed ability.
Data: Pokémon Showdown (smogon/pokemon-showdown) · commit d601443 · Data & methodology