After defeating Colress and the Shadow Triad aboard the Plasma Frigate, use the stairs to the south to reach another area of Giant Chasm.
Enter the Chasm
Go south twice, then east, north, east, and north. From there, go east, south, west, south, east, and north. Then go down the stairs and go east, then south, east, south, and east down some stairs. In the normal forest area, go east, then north to reach some stairs up to a cave. Inside the cave, keep going north until you reach Ghetsis.
There will be some long cutscenes (but they're worth watching!) and then you will be face to face with Kyurem!
Kyurem
In Black 2, you have to battle Black Kyurem. In White 2, you have to battle White Kyurem. But you can't catch it right now (you'll be able to after beating the game), so your goal right now is to knock it out.
Kyurem is weak to Fight, Steel, Rock, and Dragon moves.
Against Black Kyurem, Magneton/Magnezone and Excadrill have strong defense and can use super-effective Steel moves with a same type attack bonus.
Against White Kyurem, Jellicent/Frillish and Litwick/Lampent/Chandelure have strong defense.
After defeating Kyurem, it separates from the legendary Dragon, and Ghetsis battles you.
Ghetsis
Ghetsis has a level 50 Cofagrigus, a level 50 Seismitoad, level 50 Eelektross, level 50 Drapion, level 50 Toxicroak, and level 52 Hydreigon. Here are my recommendations:
- Against Cofagrigus (weak to Ghost and Dark): Pawniard/Bisharp, Scraggy/Scrafty
- Against Seismitoad (weak to Grass): Drifloon, Golbat/Crobat
- Against Eelektross (no weakness due to Levitate ability): Krookodile, Aron/Lairon/Aggron, Probopass, Terrakion
- Against Drapion (weak to Ground): Skarmory
- Against Toxicroak (very weak to Psychic, weak to Flying, Ground): Skarmory
- Against Hydreigon (weak to Fight, Bug, Ice, Dragon): Cobalion, Lucario, Pawniard/Bisharp
After you defeat Ghetsis, he will despair at being defeated twice now by an unknown trainer. N speaks of what he has learned about people's relationship with pokémon. A Shadow Triad member disappears with Ghetsis, but leaves behind his staff. N flies away on the legendary Dragon.
Hugh arrives and asks what happened. You can answer however you want. He tells you how to get to Victory Road so you can challenge the Pokémon League.
Explore the Chasm
The Plasma Frigate is gone and the ice has thawed. There are a bunch of broken trees where the frigate and ice were, and there are some items that you can now reach in this area.
Exit the cave and go outside. Follow the path until you can go to the left. You can see an item to the left, but the broken trees block access to it. Go south until you can go farther west, then north, then east to get the item that you saw. It's a PP Up.
Go to the southwest, past the big crater in the middle of the chasm, and you will see Rood and the ex-Plasma Grunts. Southwest from them, there is dark grass. Go south through it, then east through a maze-like path to reach a Star Piece at the end.
Go west from the ex-Plasma guys through the grass, and go north in this area to get TM03 Psyshock.
Go to the area north of where you got Psyshock, then go west. Jump down the ledge and go northeast, until you reach the base of the mountain. Go west to find a Carbos. From there, go east. Before jumping down the ledge, go south and east to get a Sun Stone. Then jump down that ledge near the Sun Stone.
Go back to Rood and the ex-Plasma Grunts, and go south, then west. The trees that you walk past have a hidden grotto in them.
You have found everything here, so your next destination is Route 23.