I posted it as a comment on that video last year but I think nobody saw it :x

Here's a copy & paste with formatting edits (I left out the very last sentence from the original comment since it's not really contributing to anything):

Transcribed lyrics with some help from an earlier comment here, hope this helps those who want to enjoy singing along. (No guarantees on accuracy though)

REFRAIN: Splat! Splat!! Splat!!!

Splatoon's the game, only on Wii U Make a mess, is what you gotta do You can splat the wall, splat the floor Splat each other, splat some more! The team with the most ink splatted will win Now you know the rules so come on let's begin!

You're an inkling kid that can change to a squid Dive into the ink; no one will know where you hid You can slip through the gates, you can swim really fast You can climb up walls, you know it's always a blast! You can charge up your ink meter too Become a kraken; see what it can do!

CHORUS: Come on! Splat the world together! Come on! Splat the world, alright! Ink it up to the sun, ink it up to the moon! Splat-at-at-at-at-at-at-at-at-at-splatoon! (at x9)

REFRAIN

The Splattershot fires rapid and wide With the Splat Roller you can really glide Splat Charger inks a long straight line Splat Bombs explode after a little time When the Inkstrike comes, hope is on your side It's a massive inkbath so run and hide!

So many spaces to claim in this turf war Like Saltspray Rig, where you're all offshore Or go inside to Walleye Warehouse; you won't leave without an ink douse! Blackbelly Skatepark's a lot of fun; there're so many ramps for you to run!

CHORUS

You can help defend Inkopolis from the Octarian nemesis Some are small and some are fat, take them out with your ink splat! If you want them out of your town, you gotta take all of the bosses down!

CHORUS: SPLATOOOOOOOOON~