Nintendo has revealed on twitter that Lucas will release before E3 on June 14th and probably with three new skins and a new stage.
Lucas will be available for purchase on your console of choice for 3.99, or you can buy him on both versions for 4.99.
As for Mii Fighter costumes the Splatoon Costume will be releasing on the same time along with a squid Inkling hat and a K.K. Rider skin all for the Gunner Mii.
What the japanese twitter of Nintendo says is that the Miiverse stage will release on the same date as the rest. satisfying
Here are the new costumes:
