Sorry if this is a little bit too much, just figured it'd be nice to have a little more for ya since I was already making suggestions, but I think the banner's lovely in its own right, too!

Some explanation(s):

• All the hashing is just some subtle shading, pretty much
• All the red is some edits going top-down, left to right:
  • Make the clouds more definitive and in 3's to make them seem a little more natural
    • With some mild shading that follows the "height" subtly of the top of the cloud
  • Make the c/splatoon part more wavy in the water and leaning only slightly towards "splatoon", in the air
    • Or just putting it all in the air after moving the characters a little, too, potentially
  • Make the boat in the background a little more transparent and maybe move it around some after editing the text
  • Push the shoreline downward so it takes up a little less real estate and looks flatter to appear more like it continues outside of the frame
    • Also makes the eye more drawn towards the art and adds some flow to the pic too
  • Move the left character to the right to fit a little more text; and potentially move the island right, too, so that it feels like it's cut off to the right
  • Squeezing the left character's arm in a little since it seems a little too oval-y, to me
  • And maybe changing the receiving end to a squid/octopus so it feels a little more blobby/shapey and pointed (and fun way to show a mechanic? haha)

Either way, I think it's super cool what you've done so far and I'm mighty looking forward to what you can do in the future, too! :D

Edit: forgot to mention also making the waves come out from the shore lines a little more (in sets of odd numbers for that made-in-nature aesthetic!), with some foam/reflective, white coloring to them, too, potentially. 👍