Announced during Splatoon Koshien 2017
Here’s the North American trailer:
Will be available in a dual pack for $24.99 in July 8th. They’ll perform songs for you when summoned. These include songs not previously included in Splatoon. If you want to listen to them check them out on this post
Also coming are color variants from the original Splatoon amiibo line sold separately or in a bundle for the normal MSRP.