Steel Diver

Steel Diver is a unlockable stage in Super Smash Flash 2 named after the eponymous submarine from Nintendo 3DS's game of the same name. It is unlocked by self-destructing with any character in the water of Gangplank Galleon, Lake of Rage, or Planet Namek 20 times.

Despite being confirmed in SSF2 Dev Blog #8, it was leaked several months beforehand when a couple of SSF2 beta screenshots were uploaded on LightShot.com. However, due to the lack of notoriety and distribution of the same, not all the screenshots came be recognized and the leak did not spread.

The stage is unique in the sense that it is an underwater stage, which makes characters jump higher and fall slower. This can be disabled by using the hazard switch, which makes the physics normal like the other stages.

Origin
The Steel Divers are a naval task force assigned to combat a power-hungry nation bent on conquest. While a wide number of vessels are under their command for the player to control, this particular model is an ND-03 Blue Shark, a mid-range, all-purpose sub with balanced attributes. Interestingly, however, it is not the default sub available; it can only be used in the Premium version of Steel Diver: Sub Wars.

Layout
Battles take place on top of the Steel Diver. Players fight on the husk of the submarine. The form is rather simple: a prolonged platforms with two edges on the side and a conning tower in the middle. The left portion is a bit slanted downwards.

Trivia

 * Steel Diver appears in Super Smash Bros. for Nintendo 3DS and Wii U as an item that can shoot small torpedoes at opponents.