|Game(s)||Newer Super Mario Bros. Wii|
Newer Super Mario Bros. Wii Plus
|Previous level||(D-3) Spine Springs|
|Next level||(6-3) Fog Cemetery|
Toxic Fortress (or World D-) is the final level in Crystal Caves. This is also the final fortress level in the game. It is unlocked via completing D-3: Spine Springs and finishing that will unlock a shortcut to 6-3: Fog Cemetery. This level takes place in an underground fortress filled with poisoned water. Some of the floors/walls drop upon touch, so be careful. There is no boss in this level as with all of the lettered world fortresses.
- Star Coin 1: Activate the switch before it's obscured by the poisoned water to reach the coin.
- Star Coin 2: Before the checkpoint, quickly reach the star coin before the platform obscures it.
- Star Coin 3: You'll need to activate the Yellow, Green, and Red Switch Palaces to access the warp pipe before the flagpole. Once inside, watch out for the spike balls and use the empty platform to reach it.