There is a monster type that only appears in this particular Yu-Gi-Oh! game. It is called immortal, and all Immortal monsters can move in and out of Crush Terrain freely. When destroyed they turn the surrounding spaces into Crush Terrain.

The Immortal type monsters are the Carat Idol, Electromagnetic Bagworm, Jowls of Dark Demise, Moisture Creature, Mucus Yolk, Rigorous Reaver, Servant of Catabolism, Shapesnatch, Slate Warrior, Souleater, Timeater. All but Carat Idol have a real card equivalent.

A common theme in the OCG/TCG artwork of the Immortal monsters is that they don't show the entire creature, only showing a part of it. However, it's possible to see their entire form in 3D models in some of the other Yu-Gi-Oh! videogames.