What is that we hear, from deep within the digital ocean? Is it the protracted bubbling whinge of superheroes in their death agonies? Are we witnessing a Götterdämmerung of the superhero movie, as a bunch of B- to A-listers, dressed sheepishly in their tattered spandex, crouch on the green screen sound stage, furtively making calls to their agents between takes and wondering if they shouldn’t have held out against superhero films, like Julia Roberts and Leonardo DiCaprio? I have often enjoyed superhero films with all their surrealism, melodrama and comedy and I actually liked The Marvels with Brie Larson. But there is no doubt about it: where the first Aquaman movie was in enough trouble, with Jason Momoa smirking his way through the story of Aquaman’s undersea travails as if guesting on a lager ad, now we have a terrible sequel, again directed by James Wan, reportedly the final film in the DC Extended Universe. The Aquaman franchise is just flatlining, floating through the dreary depths like the kind of discarded plastic bag which is going to choke the last remaining vaquita porpoise. Once again, Jason Momoa is back with his blandly self-admiring Aquaman, in the supposedly comedy-lite mode borrowed from Taika Waititi’s Thor films; the alpha-superhero with a cheerfully laidback home life. Aquaman is always hanging out with his dad Tom (Temuera Morrison), drinking conspicuously branded cans of beer from the fridge. Aquaman is now in charge of Atlantis and he has imprisoned his wicked half-brother Orm, the guy whose awful plans for amphibious domination created such non-drama in the previous film. It’s a role which Patrick Wilson reprises with an air of icily affronted dignity which is only partly intentional. The queen of Atlantis is Mera, played by Amber Heard (an actor whose steadfastness in standing up to online male bullies has to be respected) and Dolph Lundgren is once again Aquaman’s father-in-law Nereus. Willem Dafoe, who kept his self-respect in the last film playing Aquaman’s mentor Vulko, doesn’t appear, but Nicole Kidman shows up again, taking the DC shilling as Aquaman’s willowy and distraite mother Atlanna. The deal this time around is that Aquaman has become a dad, of all the adorable things. There are loads of shots of Momoa with a real baby, changing nappies and getting weed in the face by the cherishable little tyke. The trope of the tough guy sporting the baby papoose is very often used as a tired relatability short-cut by Hollywood. So it proves again here. Now Aquaman has to face the second-banana villain from the previous film, here upgraded to premier banana status. This is Black Manta, played by Yahya Abdul-Mateen II, who has among his entourage a bullied marine biologist called Dr Shin, a role in which the gifted comic actor Randall Park is entirely wasted. Will this titanic confrontation involve a rapprochement between Aquaman and his troubled semi-sibling Orm? Who knows? Or, more to the point, cares? At the end of 124 long minutes, both film and audience are deeply immersed in something – but it isn’t seawater. Aquaman and the Lost Kingdom is released on 21 December in the UK, 22 December in the US, and 26 December in Australia.