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Planes of vulnerability in Commander Keen 5

In this essay Pieter Smal discusses the planes of vulnerability in id Software's ultimate platformer.

1. Introduction
Commander Keen 5: The Armageddon Machine is my personal favourite game in the Commander Keen series. Although essays should not be stimulated by subjective opinions, my preference for the title is stimulated by interesting design choices. In this essay, I wish to discuss game- and level- design with regards to planes of vulnerability in Commander Keen 5. These planes are the horizontal, vertical, and diagonal directions in which the players traverse, whilst vulnerability refers to lethal encounters with enemies or obstacles.

id Software needs no introduction; the genius of John Carmack's engine development is known today for Wolfenstein 3DDoom, and Quake. His initial success was not the engines for these games, but his Adaptive Tile Refresh technique implemented in the Commander Keen series (see videos below). id Software developed Commander Keen in two trilogies (Invasion of the Vorticons and Goodbye, Galaxy!). A third trilogy was planned but cancelled due to the development of id Software's next groundbreaking game, Wolfenstein 3D.

Video 1: The History of id Software [development up to Commander Keen]

Video 2: The History of id Software [departure from Commander Keen]

The release and development of the Goodbye, Galaxy!  were troubled with development and publishing problems. Commander Keen 6: Aliens Ate My Babysitter did not follow the plot of the trilogy, and it was developed before Commander Keen 5. Tom Hall, who designed levels for all the Commander Keen games along with John Romero, comments:

Deciding on the tilted perspective made things look really cool, but the levels look a lot longer to make. I think the overall art design was a lot cooler, though [...]  I had done most of the art in the original Keen trilogy. With Adrian [Carmack] working on this new set of Keen, his skills honed over many games, the art was looking awesome. We did Keen 4, then Keen 6 (Aliens Ate My Baby Sitter), and then Keen 5. We did Keen 5 in one month. That was an amazing amount of work, but it's probably my favorite [sic] Keen [...].

(3D Realms S.A.)

As stated by Hall, the second Commander Keen trilogy vastly improved upon the game graphics of the original trilogy: a tilted perspective, along with detailed artwork, enriched the playing experience. Instead of a solid background, the backgrounds for the second trilogy comprised of intricate tiles. The design of the Commander Keen series is daring, but especially the second trilogy. Although the Commander Keen series is accessible (to children in particular), certain designs for both trilogies fringed on the absurd! Although the Dopefish is now a popular reference (as an easter egg) in many contemporary video games, other game enemies are more obscure in an extra-terrestrial setting, including the character of Princess Lindsey, a levitating NPC whose magic wand resembles that of a tooth fairy! The final Commander Keen [1], as the ultimate installation in this game series, contains believable enemies that fit the setting of a spaceship adventure. I particularly refer to the robotic enemies on board the Omegamatic [2], with regards to the Little Ampton, Robo Red, Shikadi Mine, Sparky, Sphereful, and Spirogrip (below). Although all images henceforth are taken from the (2017) Commander Keen wiki, I will not reference these images academically since they originate from wiki stubs.

Figure 1: Characters and enemies in Commander Keen 5

Figure 2: Fatal obstacles in Commander Keen 5

2. Planes of vulnerability
Most platformer games are two-dimensional, running on an X- and Y- axis. It does not mean that the graphics are flat since a Z axis is introduced in the Commander Keen series [3]. However, since the player does not access the third-dimension during gameplay, the Commander Keen series remains a 2D platformer. The player moves the protagonist, Billy Blaze ("Commander Keen"), on the screen horizontally, vertically, and diagonally. Likewise, certain enemies move on these planes as well. My interest in the game- and level- design of Commander Keen 5 is the player's movement on these planes. Cognitively, the player must navigate fatal enemies and obstacles on these three planes and move the avatar accordingly.

Before addressing the planes of vulnerability, the movement of each enemy must be assessed. The Korath will be excluded from this description since it only appears in a secret level and is not fatal to Keen [4] in any way. Little Ampton is not fatal on the horizontal plane, but it will kill Keen if he is on a pole (vertical plane). The Little Ampton also pushes the player on the horizontal plane. Touching Robo Red is fatal, and he shoots out bullets diagonally. Since Robo Red moves on the horizontal plane and the range of his bullets are limited I will describe his threat on the horizon plane. Like Little Ampton, Shelly will push the player on the horizontal plane. Keen will be killed if the player jumps onto Shelley, and Shelley will fatally dive on Keen if he stands underneath Shelley. The Shikadi Mine follows Keen by floating through the air, exploding when near the player.

The Shikadi are fatal horizontally, sending deadly energy rays up poles. The Shikadi Master can teleport between different areas of the level (it appears in the closing stage only), shooting out energy balls that will kill Keen. The Shockshund is also fatal, jumping high (moving horizontally and vertically at the same time), and "barks" out lethal energy bits. The Slicestar moves either horizontally or vertically on a set trajectory, although a few move on a random diagonal trajectory. Sparky moves on the horizontal plane, occasionally charging at Keen. Like the Shikadi Mine, the Sphereful floats in the air, following keen. Spindred moves up and down on the vertical plane. Spirogrip moves quickly on the horizontal- and vertical- plane, killing Keen if he is in the way. Volte-face moves on a set (usually square) trajectory.

In conclusion: Keen can touch Little Ampton and Shelley without dying, but they can kill Keen on the vertical plane. Little Ampton, Shelley, Shikadi Mine, Shikadi, Shockshund, and Sparky can be destroyed, whilst Robo Red, Shikadi Master, Slicestar [5], Sphereful, Spindred, and Spirogrip are invulnerable. Shooting Volte-face will only stun it for a few seconds.

3. Levels and game areas
Figure 3: In-game illustration of the Omegamatic 

Figure 4: The Omegamatic as the world map

The player enters the Omegamatic from the bottom of the map (figure 4) [6]. Moving upwards, the player passes through the levels of Ion Ventilation System, and the Security System. After going up an elevator, the player has the option of accessing four levels (the Energy Flow System, Regulation Control Center [sic], Neutrino Burst Injector, and Brownian Motion Inducer) that each protects a machine that Keen must destroy. Each of these levels is guarded by a preceding level, a Defence Tunnel- (named Vlook, Burrh, Sorra, and Teln). After finishing these levels, the player can access a second elevator that will take the player up to the closing levels: the Gravitational Damping Hub, and the Quantum Explosion Dynamo. On the right-bottom of the map is a secret level outside the Omegamatic. I will not discuss this secret level since there are no obstacles related to the discussions in this essay.

4.1. Navigating the planes of vulnerability
As the player moves the avatar on the screen they must plan a strategy for overcoming enemies or obstacles. My analysis will not focus on problem-solving since it is outside the scope of this study [7]. Instead, I want to address the design of enemies and obstacles with regards to the planes of vulnerability.

An unaltered screenshot of each level will be presented followed by my analysis. I will not highlight every enemy- and obstacle- encounter, but focus on the level design of lethal encounters with relation to horizontal-, vertical-, diagonal-, and free-floating- planes. Dangerous areas will be highlighted with red, whilst safe planes of movement will be marked in green. Diagonal- and free- movement planes will be indicated with a circle. Additional notes are indicated in orange. The screenshots on the website are taken in normal mode; my analysis will focus on hard mode. Subsequently, some enemies will only be described in my analysis and will not appear in the screenshots. Analysis will be marked numerically, following a typical gameplay trajectory from start to end.

4.2. Ion Ventilation System
Figure 5 and 6: Map and analysis of the Ion Ventilation System

In figure 6 (above) the player is immediately introduced to a horizontal plane of vulnerability (point 1). At point 2, the player is introduced to the vertical plane of vulnerability with Little Ampton sliding up and down the pole. At point 3, the player is introduced to the laser cannon that shoots downwards sporadically. Finally, Sphereful floats at point 4, introducing the player to free-floating enemy encounters.

4.3. Security Center
Figure 7 and 8: Map and analysis of the Ion Ventilation System

The Security Center [sic] introduces the player to more advanced planes of vulnerability. At point 1 the player is immediately faced with lethal planes that overlap: horizontal- and vertical- movements. Two Slicestars move up and down, Little Ampton slides up and down a pole and Sparky moves left to right and back. The player must decide how to overcome these obstacles.

At point 2 the player is introduced to the diagonal movement of Sparky. Although the player can avoid Sparky by jumping on the pole, Little Ampton will soon slide on the pole. Next to the pole is a laser cannon, doubling the vertical plane of vulnerability. At point 3 Sparky is in blocking horizontal- and vertical- movement of the player. The player must confront Sparky vertically without touching the robot, a recurring design concept in Commander Keen 5.

4.4. Defense Tunnel Vlook
Figure 9: Map of  Defence Tunnel Vlook

Figure 10: Analysis of Defence Tunnel Vlook

At point 1 there is a Spindred bumping up and down whilst Sparkies patrol the area below. The player must time their descent before plunging down. At point 2 the player can take two paths towards level progressing; the lower path will force an encounter with Robo Red and Little Ampton sliding on the poles. The player must face a vertical encounter with Sparky at point 3, but now with the threat of Little Ampton sliding up and down the pole. At point 4 three Spindreds bounce whilst a Sparky patrols the horizontal plane. Point 5 is the most interesting area in this level: multiple fire helices on the floor with laser cannons shooting down. To traverse this area, the player must activate a free-moving platform. The jagged movements of the platform along with the laser cannons make this area dangerous; the player must calculate laser cannons' activation time whilst remaining on the moving platform.

4.5. Defense Tunnel Burrh
Figure 11: Map of Defence Tunnel Burrh

Figure 12: Analysis of Defence Tunnel Burrh

The player faces a double verticle lethal plane at the beginning of the game: Splicestar with Little Ampton on a stick (point 1). Point 2 features one horizontal- and three vertical- vulnerability planes. Whilst Robo Red patrols the room and Little Amptons slide up and down, a third menace lurks in this room: the Shikadi Mine. Whilst Splicestars move horizontally, the player must time their descent at point 3.

4.6. Defense Tunnel Sorra
Figure 13: Map of Defence Tunnel Sorra

Figure 14: Analysis of Defence Tunnel Sorra

Tunnel Sorra opens with five Splicestars: one moving horizontally, three vertically, and one Splicestar bumping diagonally (point 1). Point 2 is not particularly difficult to traverse, but the shape that the vulnerability planes form is interesting: A square, two vertical planes, and a horizontal plane. The player must momentarily slip pass a Volt-face at point 3 to get a key, whilst point 4 is a dangerous place: Robo Red, Little Ampton, and Sparky patrols the area.

4.7. Defense Tunnel Teln
Figure 15: Map of Defence Tunnel Teln
Figure 16: Analysis of Defence Tunnel Teln

Defence Tunnel Teln opens with an immediate threat - from above! Robo Red is patrolling the area while Shelleys (point 1) are ready to bomb onto the player. Reaching point 2 is not of vital importance, but a nice area to visit if the player can figure out how to get there: three Splicestars patrols this area horizontally. The trick is to pass through the Splicestars without destroying any of them. Finally, a Splicestar bounces diagonally at point 3.

4.8. Energy Flow Systems
Figure 17 and 18: Map and analysis of Energy Flow System

At point 1, the player stands on a platform moving clockwise along the black track. Like point 5 at Defence Tunnel Vlook, the laser cannon can shoot any moment at Keen. At point 2 the player is faced with several enemies: Sparky, Shikadi, Shockshund, and a laser cannon shooting from above. With two inclinations and the laser cannon, the planes of vulnerability form the shape of a downward arrow. Although the player can jump to the ledge at point 3, the player must time this jump accurately.

Notes: John Romero hid his name on the bottom of the level. A swastika can also be seen - a hint at id Software's next project, Wolfenstein 3D.

4.9. Regulation Control Center [sic]
Figure 19 and 20: Map and analysis of Regulation Control Center

A laser cannon shoots down on a switch at point 1. This is my personal favourite design in the entire series; the player must calculate their time under the laser, pull the switch, and move before the laser shoots a bolt. At point 2 the player must climb up two poles whilst avoiding three vertically moving Splicestars and a diagonally bouncing Splicestar. The novice player will fall straight down at point 3, facing a Little Ampton, Shikadi, Robo Red, and Sparkey! The advanced player might want to skip this part by grabbing onto the ledge and going right (as indicated by the green horizontal line at point 3). At point 4 there are three Shikadis shooting lethal energy bolts up the poles. Point 5 features a Shockshund, Sparky, and two Shikadi Mines. The Shikadi Mines are of special interest: there are four red rectangles that rotate. The player can hide underneath one of the rectangles and avoid the exploding mines, but if the rectangle rotates pieces of the mine can fall on the avatar and kill Keen.

4.10. Neutrino Burst Injector
Figure 21 and 22: Map and analysis of Neutrino Burst Injector

At point 1 the player is faced with Shelly and a Splicestar; the player can jump over both as indicated by the green lines. Three Shockshunds and a Shikadi appears at point 2; the interesting design of this area is that the Shockshund jump on the player from above! At point 3 the player is faced with a Shikadi patrolling the horizontal level as well as two Splicestars bouncing diagonally.

4.11. Brownian Motion Inducer
Figure 23 and 24: Map and analysis of Brownian Motion Inducer

The player is immediately faced with peril at point 1, traversable with three platforms. At point 2 the player must avoid a bouncing Splinestar without falling off the platform and touching the fire helices. Point 3 presents at least three horizontal planes of vulnerability, intensified with the addition of a Shockshund. The player can safely move on three poles at point 4 but must avoid two fatal planes: a laser cannon and fire helices. Point 5 is of interest, where four Shelleys can explode onto the player from above.

Note: Tom Hall hid his name on the bottom of the screenshot in figure 24, marked in orange.

4.12. Gravitational Damping Hub
Figure 25 and 26: Map and analysis of Gravitational Damping Hub

Entering the level, the player is immediately faced with a new foe unique to this level: Spirogrip (point 1). Although the movement of this enemy is not limited to the lines that I drew, it gives an indication of where Spirogrip can move within this room. Likewise, the long red vertical line at point 2 only indicates a possible trajectory for Spirogrip. Avoiding Spirogrip, the player must traverse upwards on two platforms (movement marked in green) whilst avoiding the Fire Helices (square). The movement of the bottom platforms is anti-clockwise, indicated in orange. At point 3 the player must traverse the shots of multiple Laser cannons with the help of two platforms. Point 4 [8] includes a Spirogrip and a Splicestar moving horizontally. Two Volt-faces move along a rectangular pattern at point 5, and four laser cannons wove bolts together at point 6.

4.13. Quantum Explosion Dynamo
Figure 27 and 28: Map and analysis of Quantum Explosion Dynamo

Journeying upwards, the player must pass through six laser cannons at point 1. Nine Shockshunds and a horizontally moving Splicestar plague the player at point 2. Point 3 features three Shikadi's shooting electric bolts up poles; note that the poles are different lengths. The Shikadi Mines at point 4 is an unusual surprise since they serve a function beyond the destruction of the player in this level [9].

5. Conclusion
Although drawing lethal lines (planes of vulnerability) is not a design necessity, it helps to simplify the design process. In this essay I have shown how these lines contribute to the planning and placement of enemies in relation to the player on the X- and Y- axis. I propose that designers use planes of vulnerability in the design process to assess the location of dangers in video games, especially in platformer games. Although the (possibly) predetermined movements of enemies can be designed rationally, drawing lines visually helps to place the location- (and sometimes the purpose-) of each enemy in perspective.

Despite the whacky enemy designs for the Commander Keen series, the designers showed an evolutionary growth between the first and last Commander Keen game. These games should be analysed carefully, but not judged too harshly: id Software made these games in a very short period of time. The Swastika in Commander Keen 5 is only a single sign of the repressed desire to make adult-oriented games. The pyramid containing an eye in Commander Keen 4 (named "Pyramid of the Gnosticene Ancients"), NPCs known as Oracle Council Members, and the musical quotation of Mars [10] (from Holst's The Planets) in the closing level of Commander Keen 5 are all pointers towards a desire to create mature content; this desire would be fulfilled in id Software's future games, Wolfenstein 3D and Doom

1. Commander Keen 5, the last game to be developed in the series.
2. The Omegamatic (also known as the Armageddon machine) is a giant spaceship that acts as the game setting for Commander Keen 5.
3. A "titled perspective" (as described by Tom Hall).
4. Instead of Billy Blaze or Commander Keen, I will address the avatar abbreviated as Keen henceforth.
5. Slicestar can be killed with 20-50 bullets, making it almost invulnerable.
6. Keen's spaceship can be seen parked on the bottom right of the Omegamatic.
7. Problem-solving would be typical of a guidebook, cheatbook, or walkthrough!
8. Point 4-6 is only accessible if you wish to visit the secret level Korath III Base.
9. Spoiler: The Shikadi Mine is used to destroy the Armageddon Machine.
10. The quotation of Mars is a subtle indirect hint to Star Wars; John Williams' score for the original Star Wars film borrows from Holst's orchestral suite.

3D Realms. S.A. A Sequel? [Online] [18 July 17]. 2017. Main Page. [Online] [18 July 17].

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