Pokémon GO is hosting a Raikou Shadow Raid Day on Jan. 24 from 2 p.m. to 5 p.m. local time, putting Shadow Raikou in the spotlight for a limited window. During the event, players can earn up to five additional free Raid Passes by spinning Gym Photo Discs, making it easier to jump into multiple raids without spending extra. Expect the usual raid-focused bonuses and a strong incentive to team up locally. If Shadow Raikou is missing from your collection or you want better IVs, this short event is the best chance to grind.
Source: Official Pokémon GO blog and Pokemon.com