This one’s just some stupid derpy humour.
The bizarre Atlantean mutant named Sal Monn (who the humans refer to as Salmon after a miscommunication) thinks of himself as a great villain. A would be world conqueror who is on the cusp of domination.
He is, in actuality, little more than a nuisance whose plans never amount to anything at all. He once attempted to invade the land but all he accomplished was knocking over a few sand castles before he had to dive back into the sea to avoid suffocating.
Salmon considers himself to be Riptide’s nemesis but his plans to best his hated foe fall very short of ever working and Salmon has actually helped Riptide on a number of occasions. Mostly accidentally of course. Rip just feels bad for the guy and plays along.
Maybe one day the great and powerful Salmon will achieve world domination but…probably not.