Between Nintendo's E3 presentation and the demos available for Super Smash Bros. Ultimate at several Smash and FGC events, we've seen plenty of footage of the game and its characters. Delzethin has put together another moveset analysis video, this time focusing on the Inkling. Much like his Ridley video, this one isn't concerned with exact frame data or damage and knockback values, just what potential utility each move could have.
On top of their two passive mechanics, the Inklings seem to have a higher focus on ground game, at the cost of options in the air - they have quick ground movement, decent tilts and a fast dash attack, though they have a relatively floaty jump and slow aerials, which may hinder their ability to escape from juggles. Out of their specials, it seems like Splat Roller might end up being central to their game plan - not only does it allow them to quickly close gaps, but it buries grounded opponents on hit, and the ink it spreads on the ground slows down opponents. Splattershot and Splat Bombs also seem useful for controlling space, and while Super Jump deals damage both at the start and upon landing, it doesn't seem to have much utility outside of recovery.
All in all, it seems like their game plan will likely be a faithful translation of Splatoon's gameplay to a platform fighter environment - limit your opponent's movement options and keep them covered in ink to bolster the effectiveness of your own tools.