The eight-sided Polyhedral Goal Explosion is a part of Rocket League’s New Season 10 Black Market Rewards which released on 8th March 2023.
In addition to the unpainted variant, the additional variants are Black, Burnt Sienna, Cobalt, Crimson, Forest Green, Grey, Lime, Orange, Pink, Purple, Saffron, Sky Blue, Titanium White. As is the case with all tournament rewards in Rocket League, this item too is not player tradeable. Besides Polyhedral Goal Explosion, the Season 10 Tournament Reward Pool also features Corbital Goal Explosion and Moentage Inverted Wheels.
Here is a short clip showcasing the default and the painted variants of Polyhedral Goal Explosion.