As the name suggests, it is a sinister, subterranean area beneath the mortal world, filled with boiling magma and twisted creatures. The area has infrastructure inside it, but is mostly composed of bricks or metal.
Like all other chapters in Super Meat Boy, it consists of 20 Light and Dark levels, four warp zones and a boss. Only 17 light levels are need to be completed to fight the boss. This chapter is the turning point of Super Meat Boy in terms of difficulty, especially in the Light World.
Hell is noticeably more difficult and complex than the previous worlds; its levels tend to be fairly cramped, with lava and saw blades everywhere (especially in the Dark World). Other hazards include spikes (although less frequently than in other worlds), lava, and strange openings that constantly spit out balls of magma that can roll and bounce around the level. New enemies include laser-firing eyeballs which swivel towards Meat Boy, and "Black Maws" which appear out of portals and explode into nine miniature versions when they touch walls. Hell also introduces red portals which transport Meat Boy between them.
Hell seems to have some sort of machinery or mechanisms in place, as rustic metals and hellish contraptions can be located throughout Hell. The area however, is mostly made of brimstone and lava. The skeletal remains of the victims lie here as well, a reminder to any visitor who dares visit here. During the beginning of the chapter, there is mountainous terrain and lava lakes, but more mechanisms and structures will appear the further into Hell Meat Boy goes. The last few levels has him go through a flooded castle like structure, made of dark brown bricks, with a metal framework.
The Boss of this world, "Little Horn", is an enormous conglomerate of these Meat Boy corpses, seemingly given life by (or at least under the control of) Dr. Fetus. He follows a set pattern of hand and head smashes. He only need to head smash three times before the boss is defeated. After the boss is defeated, the Earth is nuked and Meat Boy must explore the ruins of The Rapture.
This is the only chapter that does not have the word "The" in its name.
Like the Forest and the Salt Factory, Hell was one of the original levels of the "Meat Boy" flash game. However, its light world soundtrack, unlike the soundtrack of the Forest or the Salt Factory, is not a remix of the music in the original level. (Instead, the original level's music got remixed into the Rapture light world soundtrack, "It Ends".)
The XBLA version of "Long Goodbye" has two bandages: one on the top left and one on the bottom left, both in the fragile rocks.
Stage 8, "Weibe", is a reference to Steve Wiebe, a two-time champion of Donkey Kong. Its Dark World version, Stage 8X, "Billy Boy" is also a reference to Billy Mitchell who held the world record before Steve Wiebe took it.
This is further referenced because in the stage, the rolling lava balls resemble the rolling barrels in Donkey Kong.
Large Black Maws will occasionally not kill you if they pass you in mid-air. Only the miniature versions and the explosion when it hits the wall will consistently.
The introduction cutscene to this chapter references the NES game Ninja Gaiden.
Hell in Meat Boy Flash uses the song It Ends. This song would be used in the sequel for The Rapture.