Summons rain when switched in.
Drizzle is an ability in Polished Crystal that causes it to start raining when the Pokémon with this ability enters battle. The rain lasts for 5 turns like the move Rain Dance unless extended by other moves or abilities.
This is a useful ability for Water and Electric type Pokémon as it boosts the power of Water moves by 50% and boosts the accuracy of Thunder to 100%. Additionally, it weakens Fire type moves by 50% - so thats a no-go if you are using a Fire type!
It is found on limited Pokémon in Polished Crystal including the Lugia, Vaporeon, and Zapdos as secondary ability. Politoed has it as a hidden ability!