In each level of Graveyard Shift, the player has to defend themselves from the hordes of attacking enemies. The player should try to kill all enemies they encounter, if possible. The screen moves horizontally right, halting when the player must destroy an enemy or object.
Enemies will fire hazardous balls at the player that will harm them if they hit. The player can block these balls by bringing up their shield but outer parts of the shield will come off if hit many times. Also The player cannot shoot and shield at the same time.
Other weapons can be obtained and some are more effective on some types of enemies. Sometimes Maidens will come on to the level, and have to be protected from all harm. If they are at all harmed, the player loses health. Health can be gained back if the player attacks a potion.
If the player obtains a poison potion, is hit by a poison ball, or spider, they will receive damage and become poisoned. When poisoned, the player's target reticule and shield will rotate automatically, even when stationary.
The player's reticule will blur every few seconds, the player can still use weapons though. A purple hue will be at the edges of the screen, other than the mentioned effects everything remains the same. Poisoning lasts for about a minute.
Zombies - these come up out of the ground and may shoot slime balls at the player. To completely destroy them in a single shot, the player must shoot their chest.
Beetle flies - these fly horizontally in one direction or around in a circle and may fire slime balls
Triffid - these enemies take multiple shots to kill and fire poison slime balls that will instantly poison the player. They sometimes come out of holes in the ground, and impervious to damage whilst inside the holes.
Gargoyle - these enemies can fly horizontally, vertically, or in random motions. They can only be damaged when they open their mouths.
Spider - are small and take a single shot to be killed. They can jump off the wall to attack the player and they are often encountered in large numbers.
Spider hive - these spawn spiders, and have to be destroyed for the screen to continue moving. They sometimes appear among a centipedes; the hive takes three grenades to destroy.
Puppet armour - these are impervious to gun fire and can only be killed by cutting their strings with sword weapon.
Suits of armour - these fire spike balls and high speed and can only be temporarily stopped.
Elite zombie - these will fire a number of orange spheres and can be damaged by shooting there orange hot spot.
Centipede - these prevent the screen from moving until defeated. They slither around the screen and fire several slime balls every 10 seconds.
King zombie - is stationary and fires massive amounts of slime balls. A great amount of shots are needed to kill this boss zombie.
Gun - This is the players primary weapon. It doesn't have ammo, but it can overheat. How close it is to overheating is shown by a dark red bar getting closer to the weapon icon box. The gun shoots bullets capable of leaving holes in walls and damaging enemies.
Grenade - arms the player with explosive spheres that create a big blast when shot, and are very destructive and kills most enemies caught in the explosion.
Sword - will break after 21 uses. Can be used by clicking and dragging and is useful for taking out lines of enemies.
Slime balls - This is fired by most enemies and will take away one heart when contact is made.
Poison ball - A poisonous sphere that instantly poisons the player. It is shot by Triffids only and is the most dangerous attack, in terms of effects. The effect of the poison will make a purple glow around the screen and the gun will move around even if it is not meant to.
Fireball - A fast moving ball, orange in colour. If it hits the player, a heart of health will be lost.
Spike ball - A spiky, slow moving ball, used only by puppet armour and suit of armour.
Note: All enemy attacks can be blocked and will break off a piece of the shield if they hit a corner
This glitch only applies to Windows XP. Every time the player shields and moves the shield, taking pressure off the Space Bar will cause the shield to remain longer. If the player moves the mouse cursor around a lot, or repeatedly mashes the Space Bar, the shield may still remain, then revert to the player's target.
In some cases, the player's target may repeatedly switch back and forth between the shield. Other times, the player's entire cursor will disappear even when withdrawn from the game. The glitch can be solved by right clicking near the pause button (||), moving the invisible mouse of the screen, then bringing the mouse back on to the screen. It takes a bit of practice.
There is a glitch with the bridge that when shot, the bridge will fall on the zombies. Instead of crushing them it will appear like nothing has happened. While that has happened Zombies that were originally on the bridge will walk in mid air and some will rise out of the ground from under the bridge.
Found on Simon Hunter's website are two cut enemies from Graveyard Shift: A werewolf and a Frankenstein squid like monster. Both were probably intended to appear in the castle levels of the game, as both enemies are depicted in that setting. All enemies in Graveyard Shift are fictional creatures associated with horror, although the squid like creature doesn't seem to be based of anything, other then having a design similar to Frankenstein's Monster.