Dark Hollow

Dark Hallow is an area in Sonic and the Black Knight that appears to be created by the power of Excalibur's Scebbard and Merlina's sorrow

Story
Sonic learns Merlina's purpose for commiting such an act of devastation, transforms into Excalibur-Sonic, and battles the Dark Queen

Gameplay/Environment
The crimson-red area seems to be similar to the world the Darkspine Sonic battled Alfa Layla Wa Layla. Merlina is defeated and the Dark Hollow dissapears

Trivia

 * The Dark queen's monster bears a strong resemblence to King Arthur