Even before the Inkling was used in the reveal trailer for the new Smash Bros. game, I believed that they were overdue for an appearance. They exploded onto the scene with the initial release of Splatoon in 2015 and have quickly cemented themselves as Nintendo's new up-and-coming franchise with great free content support for the first game and an excellent sequel for Nintendo's new hardware.
The Inklings have a variety of potential movesets at their disposal. Of course, they should have the ability to splatter ink on the stage and swim through it like in the source material. They should have access to a wide range of their weapons in order to provide the most interesting adaptation possible.