Details about REAPER
Reaper is a Import Goal Explosion.
Goal Explosions are shown when the player shoots a goal. Black market goal explosions are very rare and awesome to watch. You can equip them inside the customization window in the goal explosion tab.
To get the Reaper Goal Explosion you can either open a specific crate with a key or trade with other players.
You can search for trade offers with Reaper here.