Mame 0.139u1 Rom - Metal Slug 6

In Metal Slug 6, players can unlock a special "Slug Tank Mode" by inputting a specific code on the game's title screen. When activated, this mode allows players to control a powerful Slug Tank vehicle throughout the game's levels, instead of the usual Metal Slug mech.

After some research, I came up with a feature idea related to "Metal Slug 6 MAME 0.139u1 ROM":

Is this the kind of feature you had in mind?

"Unlockable Slug Tank Mode"

A very specific topic!