How Aquaman defeated the Shaggy Man here is symbolic in so many ways. He chose to fight the Shaggy Man alone due to pride — at least that’s what Murk surmises — and he’s not far off in that estimate. Aquaman’s recent fight with Superman made the king of Atlantis doubt his current standing with the Justice League. Add the fact that he feels he should solve Atlantis’ issues on his own as a king contributed to his choice of going at it alone.
By sacrificing his Justice League ID card, the key that allows him access to the Justice League watchtower, in order to defeat the Shaggy Man, Aquaman is showing everyone that he’s prepared to be an outcast (even from his own friends) if that’s whats needed to keep his home and people safe.
From – Aquaman Vol. 8 #9
He barely survived! He is very brave to go it alone against something so far outside his power level.