The Key to Splatoon's 2+ Player Mode!

"But I know exactly why this isn't possible. With the Pro Controller person, it's impossible to Super Jump and use Special Weapons due to the lack of a second screen. Special Weapons like the Inkstrike would be unusable on it. I don't really know a way around this... but I think if Nintendo found a way to allow a second person play would be great..."

While playing on my 3DS for the first time in forever I realized how Splatoon could have a successful Turf War, Splat Zones, etc. mode for multiple players on one system! The 3DS is just that! Considering it can be used in Smash Bros as a controller I don't see why this wouldn't work for Splatoon! 

The controls would line up pretty well! Shouts, Jump, Ink Shoot/Attack, Touch Screen Use, and Squid Form could all work the same on 3DS as the Gamepad. The only thing that would need another button would be the Sub Weapon Button. On New 3DS, this wouldn't be a problem, but for standard 3DS, Sub Weapons could just take the place of the X or Y buttons.

Now to accomplish this. The 3DS would need something to link it to the Wii U Splatoon. You need to have a copy of Smash Bros 3DS to use the 3DS as a controller on Smash Wii U, so how would it work? Easy. A Free or Extremely cheap (I would hope Nintendo would make it free) Application on the eShop that would allow the 3DS to connect to the Splatoon Game. An update could add the connect feature to Splatoon. 

And there! Great Multiplayer! The 3DS even has a Gyroscope to handle Motion controls! The bottom screen would have the map and the top would either put some info on the current game or just some placeholder, as the 3DS obviously couldn't handle the match on the top screen. 

This would ensure local multiplayer Turf Wars for possibly up to all 8 people (if you have that many 3DS). And CPUs could be generated for remaining Team Members.
As for online, it could be possible, but a little less likely as the 3DS isn't usable online in Smash Wii U, so it would be Nintendo's call.

I would praise this idea to come true, as I've quite a few people want to bash it out in Turf Wars with me locally and we were unable to do so.