This is the fourth stage of Ghouls 'n Ghosts
The Crystal Forest (クリスタルの森) is inside a huge cave filled with giant bones and many spiked green crystals on the ceiling. This area has Skeleton Murderers, which attack much like before. It ends in an area with water flowing down.
The "Devil's Cave Rotten Sea" (腐海魔境, no official English name) is an area deep inside the Crystal Forest that has many spikes. It consists mostly of slopes with water flowing down, pushing Arthur. After the slopes, Arthur goes down in giant mushroom-like platforms that attempt to eat him, and ends in a lake, where he must defeat Ohme to enter the gate to Lucifer's castle.
Chapter 33 of Namco × Capcom takes place in an "Underground Lake" (地底湖), where Ohme, the gate to the castle and the giant "mushroom" platforms near the end of the stage are present.