Big Power is one of the two skins released under the Anime Nation IV part of the Anime offer. It could be purchased as part of an item deal for a limited time in early October 2020.
Big Power could be purchased for $7.99 in a deal that included 8000 coins. It could also be purchased for $19.99 in the "Best Deal!" which included the Le Smash skin, 20000 coins, 1800 DNA, two 3x XP Boosts (1 Hour) and two 3x Mass Boosts (1 Hour). It was not available for individual purchase and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.