The Light Stone and Dark Stone are key items that you’ll get from Gym Leader Lenora after defeating Team Plasma at Relic Castle. The two stones are known as the Dragon Stones.
If you’re playing Pokémon Black you’ll get the Light Stone, whereas in Pokémon White you’ll be given the Dark Stone.
The Light and Dark Stones summon Reshiram and Zekrom respectively, and are used to defeat N at his castle.
But before you’re able to receive your game’s Dragon Stone, you must first defeat Team Plasma at the Relic Castle. This battle takes place after facing off against Team Plasma at Dragonspiral Tower.
Getting the Light/Dark Stone (Step-by-Step)
Step 1: After defeating Team Plasma at the Relic Castle, you’ll receive a call on your Xtransceiver.
Step 2: Professor Juniper is the one calling, and will ask you to come to Nacrene City.
Use Fly to travel to Nacrene City.
Step 3: Now at the Nacrene City Pokémon Center, head north towards the city’s main road.
Step 4: Once on the main road, head east on the path passing behind the Pokémon Center.
Step 5: Just ahead will be Nacrene City’s Museum/Gym. Head towards the building and you’ll enter a cutscene with the crowd outside.
Step 6: Gym Leader Lenora will meet you outside here, holding the Light/Dark Stone.
Step 7: After a brief conversation, Lenora will give you the Dragon Stone (Light Stone or Dark Stone, depending on your game version).
Using the Light Stone & Dark Stone
Even though you receive your respective Dragon Stone before earning your final Gym Badge, you won’t be prompted to use it until the final face-off at N’s Castle.
The stone is used to summon either Zekrom or Reshiram, which gives you the opportunity to battle and catch the Pokémon.
But if you mistakenly defeat the Legendary Dragon Pokémon before catching it, you’ll have another opportunity to do so later in the game. After defeating N and completing the main storyline, Zekrom and Reshiram will appear at Dragonspiral Tower.
- How To Get the Light Stone/Dark Stone in Pokémon Black & White