Swarms

Swarms
Swarm Chances
Common	88%
Rare	11%
Legendary	1%

Swarms are special events where unique Pokémon appear in specific areas. Every 10 minutes, a new swarm is announced in the system chat with a message like:

[SERVER]: [SWARMS] Swarms spawned in Route 19!

Each swarm features two different Pokémon, with a 1% chance of a third, rarer Pokémon appearing as well. While you're in the swarm area, there's a 1 in 25 chance per encounter to find one of the swarm Pokémon.
To make swarms easier to find, a UI display appears above grass patches in the area, showing the current swarm Pokémon.
Some Swarm Pokémon are exclusive. If a Pokémon is marked "No" under "Obtainable Elsewhere?", it can only be obtained through Swarms or the Pokémon Roulette.

Swarms

Pokémon	Rarity of Swarm	Obtainable Elsewhere?
Scraggy	Common	No
Croagunk	Common	No
Wailmer	Common	Yes
Azurill	Common	No
Grubbin	Common	Yes
Starly	Common	No
Nosepass	Common	No
Carbink	Common	No
Dedenne	Common	No
Shinx	Common	No
Carvanha	Common	No
Sandile	Common	No
Slakoth	Common	Yes
Castform	Common	No
Mareep	Common	No
Chimchar	Rare	Yes
Litten	Rare	Yes
Beldum	Rare	Yes
Popplio	Rare	Yes
Oshawott	Rare	Yes
Snivy	Rare	Yes
Treecko	Rare	Yes
Chespin	Rare	Yes
Bagon	Rare	No
Torchic	Rare	Yes
Rowlet	Rare	Yes
Galarian Mr. Mime	Rare	No
Tepig	Rare	Yes
Fennekin	Rare	Yes
Larvesta	Rare	Yes
Turtwig	Rare	Yes
Froakie	Rare	No
Minior	Rare	No
Lickitung	Rare	No
Piplup	Rare	Yes
Mudkip	Rare	Yes
Hisuian Zorua	Legendary	No
Zorua	Legendary	No
Genesect	Legendary	No
Hoopa	Legendary	No
Shaymin	Legendary	Yes
Ditto	Legendary	No