Butcher stars a Terminator-like android sent from a mothership orbiting the Earth with orders to exterminate all of humanity.
Similar to Abuse, Butcher is a sidescrolling shooter that has full 360 degree mouse (or analog stick) control akin to a first-person shooter. The game takes place across five episodes with four levels each, along with a three level tutorial from the game's demo and a final boss.
Out of the box, there are four difficulty levels: Hard, Harder, The Hardest, and Impossible. Each difficulty after Hard reduces the player's maximum health by a third with Impossible having the player at 33.3% health, and The Hardest and Impossible remove health and armor pickups altogether. The "W.I.M.P" DLC (short for "Winning Is My Pleasure) was later released, adding a "Casual" difficulty that gives the player 400% maximum health, double the ammo, health, and ammo pickup amounts, double the enemy reaction time, and "Secret Banana Medkits."
Each level is structured much like an old-school shooter like Doom or Quake in which the player's goal is to reach the exit at the end of the level, typically through finding switches that open locked doors. Levels must be finished in a single go; death will knock the player back to the beginning of the level, although the player will begin with full health at the beginning of the next level. There are a wide variety of enemies trying to stop our protagonist, ranging from typical grunts to ninjas, sawblade wielding flying cyborgs, hulking rocket launcher-wielding monstrosities, armored police trucks, and more, each with their own behaviors and attack patterns.
The player, on the other hand, has five weapons to fight back with: a chainsaw with infinite gas, a shotgun, an assault rifle, a flamethrower, a grenade launcher, and a railgun, along with a kick to launch and stun enemies. (There is a super shotgun, but only available in custom levels.) Each weapon is effectively a tool that serve particular purposes: the shotgun is the main workhorse that gets less accurate at distance, the assault rifle fires long distance with nearly perfect accuracy, the flamethrower engulfs enemies that can deal large sustained damage at short to medium ranges, the grenade launcher can be lobbed over obstacles and deal splash damage, and the railgun is a hitscan laser that can be overcharged into the strongest damaging weapon and can also penetrate solid walls. The ammo for each weapon is surprisingly limited, however, forcing the player to not only juggle through their arsenal but also regularly rely on the close-range chainsaw.
A primary element of combat is gauging enemy reactions. Enemies will not shoot you if they are off screen, and upon seeing the player they will have an exclamation mark over their heads indicating that they are going to attack. Within this second or so, the player has time to attack first or move into cover or out of their attack range. If the player hits the enemy but doesn't kill them, the enemy will be briefly stunned, giving the player the chance to either finish the job or move elsewhere. Kicking enemies will very rarely deal enough damage to kill, but will stun nearly all enemies as well as knocking them back, which can be use to kill them via environmental hazards such as meat hooks, lava, or just falling too far.
Movement can be augmented by special tricks akin to speedrunning techniques in old-school shooters, such as grenade jumping or using the chainsaw strategically to jump higher and effectively bunnyhop. Each level contains three hidden skulls that can often require these skills, and there is a dedicated speedrunning mode that times how fast the player can get through a level. The leaderboards are presented as a histogram that places the player's time within its relative percentile on the board.
The presentation is very dark and extremely violent. Enemies can be split apart when they are killed, with their intestines roping out of them. They can also writhe in groaning agony as they bleed out, including when they are impaled through a meathook. Blood seeps into the walls and ground through the level, and permanently remain even if the player dies and has to restart the level. There are innocent civilians that can also be gruesomely murdered for health and armor pickups (though higher difficulty levels prevent that, allowing the player to kill them for fun). It is deeply nihilistic, with its ending more or less summarizing the overall tone of the game.