After you beat the elite four they will be in east Iccirus city
Once you're done battling all 3 Shadow Triad members in Black 2 in Icirrus City, the Shadow Triad will leave and will not return until the next in-game season.
Jason Grifith (who also did a Shadow Triad Member). Hope that helped :)
After you beat colress in the team plasma frigate, go to the left panel, where a team plasma member says he pretends to be tough but does not have any pokemon. In that panel you will find ghetsis who walk out of the frigate to make kyurem freeze unova. the shadow triad will appear and each one will challenge you before you can get out of the frigate and chase ghetsis.
There aren't 'legendary trainers' in Pokemon Black/White 2, but there are 'special trainers' that are high-leveled and the strongest in the game. Some examples include Alder in Floccesy Town, Cynthia in Undella Town, Cilan, Chilli and Cress in Striaton City, Benga at the Black City/White Forest, the Plasma Frigate in the P2 Lab, the Shadow Triad in Icirrus City, and the GameFreak fellows in Castelia City. Most of these trainers require you to beat the game, though.
4 because the sell pokemon white and pokemon black and know they sell pokemon white 2 and pokemon black 2
The White Shadow - 1978 Me 2-8 was released on: USA: 12 November 1979
Yes
Here are 2 lists. Serebii has a list of shadow pokemon, while Bulbapedia has the shadow pokemon and evolutions.
There are 300 Pokemon in the Pokemon Black 2 and White 2 Unova Pokedex.
Route 20 does not exist in Pokemon White, but does in Pokemon White 2.
Reshiram is not in Pokemon White you need to trade either with Pokemon Black or Pokemon White 2.
Roselia (she is in the Wood that burned)