From the Super Mario Wiki
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Ice Watermelons, also referred to as blue watermelons, are cold and frozen blue watermelons (with blue skin, red flesh, and black seeds) found in Super Mario World 2: Yoshi's Island, its remake Yoshi's Island: Super Mario Advance 3 and its sequel Yoshi's New Island. If Yoshi eats it, he will be able to breathe three blasts of ice. The ice can freeze enemies solid, which can then be smashed to pieces. In Yoshi's Woolly World, enemies that are frozen will slide along the ground when touched by Yoshi.
The Super Blue Watermelon Special Item is available in Super Mario World 2: Yoshi's Island and Yoshi's Island: Super Mario Advance 3, and the All-you-can-eat ice watermelon! Power Badge is available in Yoshi's Woolly World. Using them automatically places an Ice Watermelon in Yoshi's mouth, allowing him to have its ability at nearly any point.
Names in other languages
Super Blue Watermelon