Brinstar

Brinstar is a widely known location in the Metroid series that mostly appears in the 2D games, though a stage with the title of Brinstar has made an appearance in Super Smash Bros. Melee. Being the starting location in the the original Metroid/Metroid: Zero Mission and the first major area visited in Super Metroid, Brinstar is one of the least dangerous areas of Zebes, as the enemies here aren't particular strong, though the area would still be treacherous to anyone who ventures into it ill-equipped to deal with the numerous hazards.

In M.U.G.E.N, Brinstar has been made into a stage by various creators; NeoKamek and MackX's versions use sprites ripped from Super Metroid, Agnibyte's version uses sprites ripped from the original NES Metroid and BaganSmashBros' version uses assets taken from the Brinstar stage in Super Smash Bros. Melee.

NeoKamek's version
Using sprites of one of the rooms in Upper Brinstar taken from Super Metroid, NeoKamek's version of the stage has the room in the background while combatants fight on a platform in the foreground that uses its tileset. The stage has many features, such as what appears to be confetti raining down on the battlefield at the start of each round that only lasts for a few seconds, and several enemies that go about their regular business, such as a Reo that flies around the stage in an M-shaped formation and the Zebs that rise out the pipe and alternate in flying either left or right. Vertical headroom is not an issue with this stage, as the relatively high boundary allows for high altitude battles before a character disappears off the top of the screen, though the stage's deltas give off the impression that vertical movement is being restricted once a character reaches a particular altitude; going up high enough with a character with such capabilities reveals an additional two Reos that mimic the behaviour of the one on the lower level and two blast doors, a blue one on the very left of the stage and an orange one on the very right.

MackX's version
MackX's version of Brinstar uses sprites of a room in Lower Brinstar ripped directly from Super Metroid, unfortunately, that particular room was a vertical corridor rather than a horizontal one and as such, there is no horizontal camera movement whatsoever, though despite the fact that the room is a vertical corridor, there is also no vertical camera movement, which leaves the stage feeling relatively cramped. The stage doesn't have many notable features outside of a single blue door on the left hand side and a single animated element in the pulsating purple thing that can be seen in the background.