Nintendo officially announced the existence of the fourth wave of Super Smash Bros. amiibo during the last Nintendo Direct in January, but has since remained very quiet about the next wave. That has now changed, as one region has officially revealed when Wave 4 will be hitting the shelves.
The Super Mario Bros. line was announced for release in March, but Wave 4 was listed as just spring. Regions outside of the US have offered pre-orders over the last month or so, but none have popped up for the US. However, that day should be coming soon as it has been revealed when the Wave 4 amiibo will be hitting one of the other regions, with the US likely soon to follow.