From the Super Mario Wiki
Spirit Mountain is the fifth level of Yoshi's Safari. It is located in the Light Realm of Jewelry Land. It can be accessed once Mario and Yoshi complete Crescent Coast. The mountain appears to be made out of quicksand except for one path Yoshi follows. Common enemies and obstacles include Bullet Bills, Paragoombas, Nipper Plants, Bob-ombs, and Spinies. The mini-boss of the level is a Sledge Bro. At the end of the level, Mario and Yoshi encountered Morton Koopa Jr. in a mechanical robot. Morton's robot looked like a frog with a top hat. After defeating Morton Koopa, the duo continued on to Grand Bridge.