Swarms

Go to Pewter City then talk to this guy that's wearing orange and black at the PokeCenter. He will say that there is a swarm of _____ and a certain route. He also says the swarm changes every 10 minutes. After that, a different swarm comes in on a different route.

Please note that swarms change every 10 minutes.

Swarms
Beldum (Super Rare)

Carvanha

Chimchar

Croagunk

Lapras (Uncommon)

Larvesta (Uncommon

Mareep

Mawhile

Mudkip

Nosepass

Piplup

Ralts

Sableye

Sandile

Scraggy

Scyther (Uncommon)

Shaymin (Super Rare)

Slakoth

Sneasel

Snivy

Starly

Tepig

Torchic

Treecko

Wailmer