Tower Defence Game Design Document


In my game, you play as a blood mage who must defend their summoning altar from an army of pesky do-gooders and knights trying to stop your plan to take over the world. To protect your interests, naturally, you summon an army of demons, monsters and more to obliterate your attackers. As blood is spilt, your power grows, giving you access to demons as strong as Satan himself.


This tower defence game allows the player to become the villain and be the one corrupting the world with monsters. The game will be split into rounds of enemy attacks. These enemies will follow a set path across the level map, that the player will be able to clearly see and follow. Before each wave, the player will have the opportunity to summon units to defend the pathway.

With each enemy defeated, the player gains a small amount of blood – this game’s currency – that they can use to summon more monsters in the future. The player can also spend blood to upgrade monsters that they have already summoned, to make them more powerful than before.

To complete the game without losing, the player must successfully defend against all the waves of enemies without letting too many through as the player will have a limited number of lives.

Game Mechanics


Tower Defence

The player must defend their precious blood altar from an onslaught of “good guys” trying to stop their grab at world domination. This brings in the tower defence theme: the player can summon units to different locations along the enemy route to destroy any enemies that come within range.


Blood mages are notorious for summoning creatures of twisted origins, created through sacrifices on their altars. I wanted to give the player the chance to experience the power of the dark arts and to revel in the magic at their disposal.


What actions can the player take in the game?

Summon Monsters

Pick a monster that you want to summon and place it if you can afford its blood cost.

Upgrading an individual monster to make it deadlier.

Dismiss Units

If a monster is no longer fulfilling its purpose, the player can banish them back to the void where they came from. This creates space that the player can use to summon other horrors.

When the player dismisses a monster, they will get a partial refund for the original summoning cost.

Pause the Game

The player can, at any time, choose to pause the game to adjust settings or exit the game.

The Story

Main Story

You were raised as a blood mage by the Cult of Cthulhu, destined to bring about the world’s end. Finally, after years of planning and preparation, your time has come. Unfortunately, the leaders of the world are none too happy about your plans to destroy it and have sent their finest warriors to defeat you, too bad you have all of hell on your side.


The game will end when the player has taken too much damage to continue to summon monsters, or when there are no more waves of enemies to defeat. If the player is defeated, the world will return to normal, and any monsters that they had summoned will escape to the void. However, if the player is victorious, the world will be overrun by the creatures that you have summoned.


Whenever the player’s monsters kill an enemy, the player gains a new supply of fresh blood to use to summon more monsters. As you defeat more enemies, your blood stores fill, allowing you to summon stronger and more powerful minions than before. You can also use your supply of blood to upgrade your existing monsters by feeding it to them.

User Interface

At any time, the player should be able to see how much blood they have that they can spend to summon more monsters, especially if the player is able to summon during an attack wave. Furthermore, when the player is considering which monster to summon, they need to be able to see a variety of information about that monster, such as cost, damage per second, damage type, and range. If the player is able to summon during an attack, then the menu for monster summons must not cover the screen at this time, or the game must pause while the player considers their options.


Start of Round

At the beginning of each round, the player will be able to use their supply of blood to summon some monsters before the enemies begin to attack. Once the player is happy with their troop placement, they can opt to start the round. This will cause the enemies to begin to follow the path.

Between Waves

After a round has completed, the player will have the opportunity to summon more creatures, dismiss any creatures they already had on the map, and upgrade their monsters. This also gives the player a chance to take a pause and think up a strategy for how they want their units placed for the upcoming attacks.

Enemy Behaviour

The monsters that you summon will have to automatically attack enemy units within range when their attacks are not on cooldown, as this is the main mechanic of a tower defence game. Furthermore, the enemies must follow a set path across the map, through the field of monsters.

Sound Effects

I want to add atmosphere to the game through the use of eerie music and sound effects. I would like to be able to work with a sound design student at another university if possible, so I can work with people from other disciplines, and practise co-ordination within a small team who are creating different parts of the same project.


Since the game revolves around summoning monsters and mythical beasts to do your bidding, I want to create a dark atmosphere to make the game feel like you are overrunning the world with evil.

I would like to be able to create most of the visual assets for the game myself where possible. I will design creatures and their attacks on paper, before transferring these ideas to a digital medium. I will use pixel art as it gives me the freedom to create simpler animations, that will require less frames.

Technical considerations


How can the player place units?

In some tower defence games, the player is only able to place units within the bounds of a grid. In others, the player can place units freely, so long as they aren’t on the enemy path, or overlapping with one another. Before I begin creating my game, I need to decide which of these two methods to use.


Future Additions

  • Time control: The player would be able to pause/play the flow of the game at any time, as well as speed up the pace of the game to make levels pass faster. This is a common feature in tower defence games.


  • World progression: As the player progresses further into the game, the time period could change. The player would start out facing knights and peasants, but as time passes, they may have to face guns, flamethrowers and more.


  • Different enemies: Inside of a wave of standard enemies, there could be a few more advanced troops, with greater armour or that move faster, to make each wave more interesting, and to encourage the player to vary their monster placement in response.