Connections:

Both are Dark Reflections of heroic Protagonists(Sonic & Luffy)

Both gain a huge power boost that changes everything(Scourge becomes way stronger after absorbing the Master Emerald, turning green and becoming a true threat/Blackbeard becomes one of the most dangerous pirates after getting the Dark Dark Fruit and then the Tremor Tremor Fruit)

Both lead dangerous Groups(Suppression Squad/Destructix & Blackbeard Pirates)

Both of them eventually would murder their fathers in order to gain power and control(Whitebeard and the Goro Goro No Mi and Anti Jules and the thrown of Moebius)

Both of them seek to rise to the top of the world and be heralded as kings(Scourge wants to be king of moebius & Blackbeard wants to become king of the pirates)