Forerunners

The Forerunners were an ancient species of aliens that were found by the Brotherhood of Makuta in which Teridax married a female forerunner and had a son named The Didact who later became their leader. They served as the arch enemy of the echidnas fighting them in the years of the 16th century and soon then their commander Lochagos was ordered by the Didact to deceive the Nocturnal Clan by making them become enemies with the Knuckles Clan and soon became their mentor and frenemy. They are the true main species of antagonist in Super Smash Bros. Brawl Crossover.

Echidna
The Forerunners have an extreme hatred of the echidnas, ever since the year of 1994, the Forerunners initiated wars with the echidnas throughout many locations such as Central America and even their indigenous home country Australia wanting to take over their home. The main reason why the Forerunners loathe the echidnas is because that they are jealous of how successful the echidnas are experiencing more peaceful and better life with technology more modern than the Forerunners and are angered at how they possess the skills of using super strength that the Forerunners are no match for. One of the generals Lochagos and the monitor 343 Guilty Spark had created Metal Knuckles a Forerunner Sentinel version of Knuckles the Echidna, they told him to defeat Knuckles and destroy or imprison the echidnas. Metal Knuckles refused to obey his creators and turned against saying that he doesn't take orders from people who consider him a pawn and was glad to created to experience life.