Icy Spike Ball
From the Super Mario Wiki, the Mario encyclopedia
Icy Spike Balls are ice-covered Spike Balls that first appear in New Super Mario Bros. 2, exclusively in World 4-1. Both normal and Giant Spiked Balls appear, and behave identically to normal Spike Balls. They can only be destroyed by Gold Mario.
In Donkey Kong Country: Tropical Freeze, Skowl, the Startling creates several Icy Spike Balls during the first phase of his battle. While flying above one corner of the battle arena, Skowl uses his ice powers to hurl Icy Spike Balls at the other corner. After landing, they start rolling slowly in the opposite direction, across the arena. In this game, they are indestructible, but can be safely bounced on with Cranky Kong's cane.