Steel Diver (universe)
From SmashWiki, the Super Smash Bros. wiki
The Steel Diver universe (スティールダイバー, Steel Diver) refers to the Super Smash Bros. series' collection of properties that hail from the Steel Diver series of naval combat games developed and published by Nintendo. Originating as a tech demo for the Nintendo DS, the player simulates controlling various war submarines with the bottom Touch Screen.
The universe makes its debut in the Smash series with an item and two trophies, one of which exclusively appears in Super Smash Bros. for Nintendo 3DS.