Princess Peach and her Toads are frozen because of Frost Bowser and his Icy Minions

Frost Bowser: Well, well, well. It seems you've stumbled upon the frosty throne of greatness. I am Frost Bowser, the coolest ruler of the coldest corners of the kingdom. Tremble before my chilliness and bow to my icy power. Pleased to meet you.

The Mushroom Kingdom Is frozen