You do not defeat Team Plasma in Striaton City, you will need to defeat them in the Dreamyard.
to get to castellia city you have to defeat the narceen city gym leader.Then go into the woods and have a team plasma battle.
lillipup and patrat but you can not breed intill you get to nimbassa city and defeat team plasma
In Driftveil City, you will find Team Plasma in the cold storage. Once you defeat a guy who is studdering from the cold, go to the left and you will see an open crate. They are in there. ;p
You get it after you defeat Team Plasma in Pinwheel Forest.
defeat team plasma at twist mountain
you defeat team plasma and get the national dex,then battle alder
If you got 7 badge and defeat the team plasma at the dragon tower (Idk what names) and got a Dark stones or light stones at the 2nd gym town. The team plasma would disappear. You can use walk through wall.
Oh you just need to battle with team plasma. Then with all the event with team plasma done for NOW in Castelia City Burg can finally battle you!
In the building across from the pokemon gym
go to the left and down they will be there
They are in cold storage below Driftveil City
When you defeat the Elite Four, there will bw a Team Plasma confrontation (Trying to avoid spoilers) and Reshiram will be revived.