The Shiver Spirit and Burn Spirit are two mysterious creatures that appear in various Mario Games, starting with the upcoming Super Mario Bros. and the Secret of the Super Star.
The Shiver Spirit is similar to a giant Lava Bubble, but is light blue rather than orange. The Burn Spirit has a more simple design (looking exactly like a giant Lava Bubble).
In fights with this deadly duo, the player must use a Yoshi to spit a fireball launched by Burn Spirit at Shiver Spirit, or launch a snowball from Shiver Spirit at Burn Spirit. Once they're hit, they'll launch three more fireballs/snowballs. After three hits on one of them, the other will leave, and you've won the battle.
The two make their first appearance in this game. They fight the player in World 4-Castle.