Metal Box

The Metal Box is an item from the  series that appears in Super Smash Flash 2.

Overview
When the Metal Box is hit by an attack, it covers the character who attacked it in metal for 11.5 seconds, turning them gray and metallic in appearance. In this form, the character's gravity is increased by a huge amount, but they also have much more knockback resistance, to the point where certain attacks do not make them flinch even if they are at high damage percentages. Additionally, every voice sound the character makes gets removed, and other sound effects, such as landing sounds, get replaced by metallic sounds.

In Classic, the second-to-last opponent the player has to face is a random opponent who is permanently metal and has 1 stock. The battle takes place in Meta Crystal and is the second Mini-Boss battle in Super Smash Flash 2. On Hard difficulty or higher, the random metal character is replaced by the Metal Bros..

The metal effect granted by this item is used in the Metal modifier in Special Smash, in which all players are permanently under the effect.

Origin
The Metal Box appears in  as one of the three Cap Blocks containing special caps that Mario can find throughout his adventure. When starting a new game, Metal Blocks initially are outlined translucent blocks that cannot be used, and in order to make Metal Blocks solid, Mario first must find and press the Green ! Switch hidden in the Cavern of the Metal Cap. When Mario opens up a Metal Box, it will release the Metal Cap, a metallic cap that he can put on to temporarily become Metal Mario, becoming impervious to damage, capable of defeating certain enemies on contact and making him so heavy he is able to walk underwater. Its transition to SSF2 omits the metallic cap and directly turns the character into metal form when hit. Additionally, whereas in Super Mario 64 the Metal Box stays in midair so Mario can punch it from below, in SSF2 the Metal Block remains in the ground so it can be used.

Trivia

 * There are two notable easter eggs regarding characters under the effect of the Metal Box:
 * will gain a unique pinkish coloration as a reference to Pink Gold Peach, a character in the Mario series. She is the only character to not get a grayscale coloration.
 * will play a metal remix of the  victory fanfare for his down taunt.
 * Mr. Game & Watch's original sprites set is actually him on his metallic appearance, which are then recolored for his costumes, including his default appearance.