From Bulbapedia, the community-driven Pokémon encyclopedia.
Whirlwind was to have been one of the starter sets from the Groundbreakers expansion set of the Pokémon Trading Figure Game. It would have been a counterpart to Skydive, and a part of Battle Starter. The Skydive starter kit appeared in Wal-Mart as early as 11/15/07 as part of a special distribution deal, but the Whirlwind starter kit was never released due to the cancellation of Groundbreakers and the discontinuation of the TFG.
As a starter set, it would have contained four figures with bases, three of which are Pokémon and one of which is a Pokémon Trainer, a two-sided playmat with a green 6-on-6 arena on one side and an orange 3-on-3 quick start arena on the other, a 2-sided collector's sheet with a how-to-play guide on one side and a figure checklist on the other, a rulebook, and three Trainer cards.