Despite having less points, this new weapon proved to be a major step up from the five-pronged weapon Arthur left behind. Now, he wasn't just able to summon tidal waves or prehistoric creatures from the depths of the ocean; Poseidon's trident allowed him to harness other godlike abilities, including creating earthquakes by controlling the sea's tectonic plates, or manipulating the weather to the point where he could summon thunder and lightning via huge storms. Most notably, Arthur could use water as a medium to teleport to other realms. In other words, he held unlimited power as an avatar of Poseidon, with the god succeeding in his intent -- to turn him into a champion and a true "Protector of the Deep," which is what we hear Momoa's Aquaman claiming to be.
This wide range of abilities could only be wielded by the royal line of Atlantis, as Poseidon didn't want his trident falling into the wrong hands, so this also ties into the hologram of what we assume to be King Atlan when Arthur and Mera discover the relic room in James Wan's trailers. It syncs up with his speech on the trident's power and also, its ability to unite the two worlds Arthur belongs to. After all, Arthur did use Poseidon's trident in the New 52 to carry out a similar mission, freeing the people of Thule and taking them in as refugees, all before he and Mera mended issues with the surface world.
Ultimately, saving Thule cost him the trident as he had to use it to destroy the witches' supernatural infection. But using Atlantean sorcery and science, he was able to create a replica with Poseidon's blessing, a weapon which could even harm the Kryptonian god, Rao.
In the New 52, Wonder Woman had a chat with Arthur on using this Greek weapon of mass destruction, especially because Poseidon wasn't someone to be trusted. But as Arthur indicated, with Neptune's power no longer able to help him, he had no choice. Eventually, he proved to her it wasn't a deal with the devil as he ultimately wielded the trident in the name of justice for all, thus putting Wonder Woman's concerns to rest.
One theory regarding the long-delayed Flashpoint film is that we may see the Amazons and Atlanteans at war. And while we doubt it'll come to this, it'll be interesting to see if future DC movies do work in Poseidon as the universe's prevailing sea god over Neptune, and how Wan manages to have him imbue all his power, and that of the oceanic kingdom, into this trident.
With all this still a mystery, one thing's for sure -- Aquaman will be attaining one of the most powerful relics in the universe, and as Mera said, he'll be using it, not to rule as a king, but to protect all realms as a hero.
Directed by James Wan, Aquaman stars Jason Momoa as Aquaman, Amber Heard as Mera, Patrick Wilson as Ocean Master, Willem Dafoe as Nuidis Vulko, Yahya Abdul-Mateen II as Black Manta, Temuera Morrison as Thomas Curry, Dolph Lundgren as Nereus, and Nicole Kidman as Queen Atlanna. The film opens on December 21.