The floor where the following battle takes place is doorway-less, save for one. Try to go through it, and Ghetsis will appear and reveal the whole plan of Team Plasma-to have everyone free their Pokémon so that Team Plasma will be the only ones to have Pokémon! He will spread his influence to other regions, so he can rule the world.
Anyhow, go north into the room, and N will soon begin to speak. After he is done, go further north to meet N, who notices that you still lack the other legendary Dragon. He challenges you to a battle, and his Zekrom/Reshiram will burst through the wall and into the room. Soon afterward, your Light/Dark Stone will respond and spawn the other legendary: Reshiram (Black) or Zekrom (White). You can save before battling. Once you're ready, battle it!
Special Encounter: #149/#643 Reshiram (Black Version ONLY!)
Level: 50
Type: Dragon/Fire
Moves:
Dragonbreath
Slash
Extrasensory
Fusion Flare
Reshiram has weaknesses to Dragon, Rock, Ground, and Water, I think. To catch it, there are several ideas I can give. You can use False Swipe (or another attack until you believe it will KO on the next one) until it hits 1 HP, then status it. From there, you should use Ultra Balls (or Dusk Balls, but I don't know if this qualifies as a dim place). And then there is just using the Master Ball from the beginning, though I would save it for another day (cough Kyurem cough).
Special Encounter: #150/#644 Zekrom (White Version ONLY!)
Level: 50
Type: Dragon/Electric
Moves:
Dragonbreath
Slash
Zen Headbutt
Fusion Bolt
Zekrom has weaknesses to Dragon, Ice, and Ground-nothing else. To catch it, there are several ideas I can give. You can use False Swipe (or another attack until you believe it will KO on the next one) until it hits 1 HP, then status it. From there, you should use Ultra Balls (or Dusk Balls, but I don't know if this qualifies as a dim place). And then there is just using the Master Ball from the beginning, though I would save it for another day (cough Kyurem cough).
After the battle, N will heal your Pokémon, and a battle will begin. Assuming you caught your legend with an empty slot, you are oddly going to use it first regardless of what your previous Pokémon was.
Team Plasma N
Pokémon:
Zekrom [Black Version only] (Lv. 52) Dragon/Electric
Reshiram [White Version only] (Lv. 52) Dragon/Fire
Carracosta (Lv. 50) Water/Rock
Klinklang (Lv. 50) Steel
Archeops (Lv. 50) Rock/Flying
Zoroark (Lv. 50) Dark
Vanilluxe (Lv. 50) Ice
Type Weaknesses and Resistances:
Zekrom is weak to Dragon, Ice, and Electric.
Reshiram is weak to Dragon, Rock, Water, and Ground.
Carracosta is weak to Grass (4x), Electric, Steel (?), and Fighting.
Klinklang is weak to Fire, Fighting, Ground and is immune to Poison.
Archeops is weak to Steel, Water, Rock (?), Ice, and Electric. It is immune to Ground.
Zoroark is weak to Fighting and Bug; it's immune to Psychic.
Vanilluxe is weak to Fighting, Fire, Steel, and Rock.
Recommendations:
With your opening legendary Pokémon, use Dragonbreath for the super-effective damage. Virizion (or a Grass starter/simian) is best against Carracosta. Scrafty or Reshiram is best against Klinklang. A Water starter or Zekrom (Reshiram is also okay) is best against Archeops. Scrafty will work well against Zoroark and Vanilluxe. Reshiram or a Fire starter or simian works well against Vanilluxe, too.
After the battle ends, N will realize that people must learn to accept the ideas of others.
Timestamps:
00:00 - Intro & Cutscenes
04:40 - Catching Zekrom
06:03 - N Final Battle
12:28 - N Final Battle aftermath