Torvus Bog
You've now explored a good chunk of Torvus Bog; now it's time to explore the Dark side of it.
Torvus Temple
Return to Torvus Temple and get to the lower part of the room if that's not how you got in. If you're in the upper part, then scan the Emerald hologram to activate the lift if you haven't already.
Scan the door with the Emerald hologram to open it and go through the door behind it. This is the door on the right if you're coming from Temple Access.
Underground Tunnel
There is a Grenchler here and it can be an awkward fight since it's tricky to get around behind it in close quarters. Before moving on, switch to Morph Ball and roll under the ledge at the entrance for a Missile Expansion.
Continue to a part of the passage with a low ceiling and switch to Morph Ball to get through. When you come out there are Sporbs waiting, so quickly switch out of Morph Ball and use Missiles on them. Get the history scan here and use the White door.
Torvus Grove
Cross this room and just before you reach the opposite door a new type of Pirate attacks. They are Pirate Commandos, the Light version of the Dark Pirate Commandos you may have met before. When you defeat them, the opposite door is unlocked so you can get through.
Meditation Vista
Use the portal here. There is a platform moving around in the distance, but it's another teaser since you can't reach it until late in the game.
Dark Torvus Bog
Gloom Vista
There's nothing here but the portal so go through the door.
Polluted Mire
Hunter Ings, a new type of Ing, are waiting for you here. Shoot them with the Light Beam, but only when you can get a target lock since otherwise the shot will just go through them. Follow the trail of platforms and ledges that circle the central "tree" to reach the Black door.
Dark Falls
There is a save station here and it's a good idea to use it because a boss battle is coming. Be sure to hop over the poison water as you come out of it.