Carter Greene
© Carter Greene 2023

GAMEPLAY DESIGN

I developed the original concept for Soul Tower, and worked alongside artists and programmers to bring my ideas to life for our vertical slice demo.

My initial core concept sketches

Final core mechanic demonstration

RESEARCH AND CONCEPTING

When initially conceptualizing Soul Tower, I began by examining past tower-defense titles and identifying the key features shared between them. By distilling the genre to its essential elements, I wanted to find ways to subvert these conventions and create a unique twist on the classic TD formula. Variables I found include…

- Perspective (top-down, side-scrolling, 3D, etc.)

- Resources (how they are acquired, what they are spent on, etc.)

- Scale (how many objectives you have to defend, playing field size, etc.)

- Control (point-and-click, free moving character, etc.)

- Enemies (how they enter and move through the space, how they attack, how their difficulty is scaled, etc.)

- Upkeep (placing, repairing, upgrading defenses with acquired resources, and how these defenses function mechanically)

My research revealed the tendency for tower-defense games to have the player’s defense be effectuated almost entirely by automatic sentries, placing far greater emphasis on resource management and strategic placement over combat mechanics. Based on this, I started brainstorming ideas for ways to more directly put the flow of battle in the player’s hands by removing automation entirely.

One concept I had involved a tower-defense game from the perspective of the tower, with players defending a separate objective from afar. This eventually evolved into the tower itself being the setting and main defense point, taking a page from games like Babel Rising.


For combat, I was additionally influenced by Dungeon Warfare 2 and the popular “Deathrun” gamemode from Garry’s Mod. The former inspired the idea of creating a gauntlet of deathtraps to keep out trespassers, and the latter informed the timing-based activation mechanics with which players defend themselves.

To contextualize the gameplay mechanics, I came up with the idea of our necromancer character who, in order to shed his mortal shell, transferred his soul into the walls of his tower lair – giving him the power to manipulate it at will.


From here the rest of the game sprung forth rather naturally. The objective to defend became the Soul Catalyst, an artifact at the top of the tower that houses the necromancer’s soul energy. The game’s currency became soul points, as enemies who died in the tower would have their life force harnessed by the Catalyst to strengthen the necromancer’s magic.


After pitching my ideas to the team and making adjustments with them, we were ready to begin development of Soul Tower proper.

SETTING DESIGN RULES

To ensure a cohesive design vision for the project, I set a number of hard guidelines for our team to follow when concepting traps, enemies, and rooms. The most important of these rules was that all damaging traps must be player-activated – no automation allowed! Every aspect of the game revolves around this central premise and thus it needed to be upheld for consistency.

Another design rule I implemented was that all enemies must die after taking damage only once. I wanted difficulty to be determined not by the size of an enemy's health bar, but by how erratically they moved to avoid traps and how they entered the tower itself.


In this way, successful defense is more dependent on proper timing and strategic trap combination than on what damage upgrades you can afford with accrued resources. This naturally makes combat more satisfying and addicting, as players can take out large groups of creeps with the click of a button if they plan and time it correctly. It also demands players pay closer attention to enemy types and movement patterns, promoting greater engagement.

I additionally set technical parameters for the design of our core game elements. For instance, all enemy types had to fit the same sprite dimensions so that they could properly fit through room entrances and doorways. I documented each of these specifications for reference by the team as we continued to brainstorm new mechanics and build out metrics prototypes.

EMERGENT INTERACTIONS

Each usable trap and room offers its own unique affordances that can be combined with other types for greater effect.


I wanted to encourage players to experiment with different interactions and develop their own strategies with the relatively few tools at their disposal, allowing for varied approaches to gameplay.

Traps vary by range, cooldown, active duration, and whether they can be placed on walls or floors. Some traps like the Ward Eye and Slime Floor are non-damaging, but offer unique benefits such as enemy alerts or slowing movement, respectively. Rooms, on the other hand, vary by the amount of trap slots within them – and some balance this with special passive effects such as the Library's 2X soul point multiplier for enemies defeated in its walls.

This philosophy of developing emergent interactions also extended to our enemy design, as I included creative methods for players to take certain enemies out. Climbers, for instance, can be defeated before they enter the tower by burning their rope with an exterior Flamethrower trap (as seen in the video above). Of course, only certain room types allow for this strategy, forcing players to weigh the pros and cons of each choice they make.

COMBO SYSTEM

During playtesting, we found that players weren’t earning enough soul points in the early game to purchase high-cost traps and rooms, limiting gameplay options significantly.


To resolve this, I suggested the introduction of a system to exponentially award extra soul points for combo kills with a single trap activation.

In addition to further encouraging skillful and attentive play, this system added extra depth to our trap mechanics and game economy. Hazards with higher combo potential were balanced with higher prices and cooldown times, giving players even more factors to consider when spending their soul points.


Should you spend your resources on a single trap with a high cooldown that will pay for itself if you can manage to rack up combos with it? Or should you buy several smaller traps with a more reliable activation rate, thereby avoiding the risk of enemies slipping past?

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