File:Inkling poster.jpg

Summary
Although not released on the Smash website like the SSB4 character posters, this was posted on the official Japanese and French Splatoon Twitter accounts, the official Nintendo Versus Twitter account and the official Splatoon Tumblr account in celebration and seems to fill the same role. One can notice the flaming Smash logo from the Inkling's reveal trailer. The art style of the poster shares similarities to the promotional posters for Splatoon and Splatoon 2.

Source
Splatoon Twitter (Japanese) Splatoon Twitter (French) Nintendo VS Twitter Splatoon Tumblr