The
Metal Slug 6 official site has been updated with the
systems section, which describes the controls and gameplay features in the game.
They also have the weapons available in the game listed on the page.
As usual, Up+D+A will allow you to use melee attacks using Ralf and Clark.
E to switch between two weapons.
From the previous alpha and beta games, the difficulty selection has been renamed from "Rare" and "Medium" to "Easy" and "Hard".