Vacant Ark

Vacant Ark(ヴェイカント・アーク in Japanese) is a horizontal doujin shooter developed by Buster in 2005 for Windows 95/98/ME/XP using Shooting Tkool 95. The game takes inspiration from past shooters such as Ikaruga, Radiant Silvergun, Darius and R-Type series with its atmospheric deep sea setting and option/weapon system. The game spans over 3 hadal zones. In addition, there are 4 difficulties. Practice, Easy, Normal, and Hard(dubbed Shallow, Middle, Deep, and Abyss respectively). The gameplay is somewhat novel. Boasting an interesting ammo system, demanding awareness and precise execution from the player.

For replay videos, visit the Video Index.

Controls

Just like many Windows games. Vacant Ark utilizes the keyboard for controls.

• Arrow Keys: navigates the menu and moves the character.
• Shift/Enter/Space: Confirm button in the menu.
• Z: Shoots weapon currently equipped. No autofire.
• X: Cycles to the next weapon(Cannon > Riot > Force). There is a small delay before the player can cycle again. So learning the timing is important.

Other controls

• Q: Quits back to the title screen or resets score and skips to the next zone(not much is understood about this function, but killing an enemy and collecting a gem seems to consistently do the latter).
• F1: Pauses the game. Game can be paused at any time.

Gameplay

The player controls a Cyborg mermaid with 3 cycleable weapons and 6 ammo chambers. Each weapon use consumes 1 ammo. When the player doesn't shoot. An option spawns on a position depending on what weapon is currently equipped. If the player is out of ammo. Then a close range low-damaging weapon is shot instead. The player always starts with 3 lives and full ammo. Lives can be increased up to 6. If all lives are lost, then the game will end and the player will be brought back to the main menu. There are 4 different difficulties each with their differences. And the run consists of Zone A, B and C each with 4 subzones with the exception of Zone C, which consists of 1 enemy wave, 1 boss, and the final boss with 4 phases.

Player hitbox

The player hitbox is placed on the chest of the mermaid indicated by the white orb. Exact size is unconfirmed.

Auto-Shield

Getting hit by a bullet or an obstacle protects the player from losing a life but empties the ammunition. Getting hit with empty ammunition will take away one life.

Weapons

It's important to note that every weapon fires in front of the player sprite and that the option position has nothing to do with where it fires. Rather, the options act as a shield that erases bullets and deals tick damage to enemies.

Icon	Weapon	Option	Description
	Cannon	Front	Shoots a fast single-targeting projectile. Deals a considerable amount of damage and has a fast fire-rate. The projectile can sometimes erase bullets while traveling but have a thin hitbox. Useful for bosses and high HP enemies.
	Riot	Orbit/Rolling	Shoots a barrage of bubbles. Deals relatively low damage but can be used as a shotgun and it can be aimed by moving vertically. Slow fire-rate and has semi-piercing property. Useful for dealing with low HP enemies.
	Force	Back	Enchants a melee range Force field that erases bullets. Destroying enemies with Force turns them into a large explosion while bullets erased turn into small explosion. Those explosions have the same effect as Force, causing a chain reaction of explosions. In vacuum the weapon deals moderate damage with a moderate fire-rate. In the right situations becomes more destructive than the Cannon.

Items

Icon	Name	Description
	Fish Gem	Acts as a score item and replenishes ammo. They are obtained by defeating an enemy, erasing bullets or after defeating a boss. Auto-collection of all gems on screen is done by cycling weapons.
	Life/2X Ratio	Life: A large red gem that increases your live count. 2X Ratio: A large blue gem that doubles your Gem Counter value. It also replenishes your ammo.

Extend/2X Ratio

After killing enough enemies. A tune will play and a Life Gem will appear in the middle of the screen. Every 3 seconds it will cycle between a 2X Ratio and a Life gem then drift towards the player. This is how the Life Gem cycle would go: Life > Ratio > Life > Ratio > Disappear. How close the player is to getting this item is indicated by a thin red bar under the live count on the top right which only increases by defeating enemies. If full lives is reached. An additional life item will give the player 10,000 points, indicated by the voice clip that says "BONUS" with the "10,000" text that displays when the life item is collected.

BONUS

Secret Extend

The red mermaid during Zone C

Upon defeating the red mermaid during Zone C. The player will be rewarded with a guaranteed Life/2X Ratio. The red mermaid has three shields indicated by the Auto-Shield sound effect before you can defeat her(she dies the same way the player game overs). The pattern she will use can be identified by the position of her option(similar to the position of the players' option). But the pattern order is fixed anyways.

Difficulties

Difficulty select

Name	Description
Shallow	A trail mode of sorts, spawns a Gem every couple of seconds. The run ends after the first zone. The Q key can still access different zones.
Middle	Easy mode, no revenge bullets. Overall slightly easier patterns and less aggressive enemies.
Deep	Normal mode, aimed revenge bullets. Larger enemies shoot a fan of revenge bullets. Some bosses are more aggressive.
Abyss	Hard mode, defeating almost all enemies does not spawn fish gems. Instead they shoot aimed and random revenge bullets. This makes the difficulty much more chaotic and Force weapon to be essential.

Because of revenge bullets in higher difficulties. The Riot weapon becomes a liability because it can put the player in danger. Thus, Force becomes essential especially on Abyss.

Scoring

Ammo and Gem Counter.

• Gem Counter: The crux of Vacant Ark's score system. The counter increases when defeating enemies and bosses. The amount it increases scales with enemy size/HP and difficulty. e.g. Middle gives +500 for defeating bosses. But Abyss gives +1000. Bosses can be dismantled. And these boss parts can increase the counter value too. The counter's max value is +25,600. The counter depletes passively and from other actions. Such as grinding the options on bullets, obstacles, or enemies. Using the Force weapon to erase bullets also has the same effect as grazing the options(despite that, it is still worth it to use force in the right situations especially in Abyss where the game gives you a lot of counter value to account for the loss). Collecting gems manually decreases the counter by 40 per item. Triggering Auto-Shield will decrease the counter by a flat amount. Losing a life will decrease the counter by 50% of the current value.
• Gem items: Gems are essential for ammo replenishment and scoring. The amount of value rewarded when collecting gem items is relative to how high the gem counter is. Note: There are some oddities with how gems are calculated. Which will be confirmed after much more in-depth analysis of the game's mechanics.
• Bullet cancels: During some boss fights. All bullets on screen turn into gems. Though, it is difficult to time it while focusing on speedkilling the boss to minimize counter depletion.
• 2X Ratio Gem: Obtaining this item will double your current counter value. With this item, it is possible to max out the counter as soon as Zone A-2.
• Boss milks: Rare in such a game as Vacant Ark. But possible. Using Force the player can damage the boss while at the same time turning a large cluster of bullets into Gems.
• Clear Bonus: The game calculates a clear bonus after finishing a run and displays it during the ending. The calculation is (lives * 1,000,000) + (Counter * 1,000). Theoretically, the lives bonus can be as high as 6,000,000. It's impossible for the counter to be at max value when a clear occurs. So a lucrative bonus of 25,600,000 is not possible.

Scoring Strategy

• Max out gem counter: This is very important as gems become lucrative throughout the whole run given the player never loses a life. Avoid collecting gems manually early on for optimization. Only 2 Double Ratio's are needed to reach +25,600 counter. In Abyss, with the right optimizations and some RNG. You can reach max counter value during the section after the 2nd boss in Zone A right before the 2nd extend drop.
• Max out lives: Once you finish maxing out the gem counter, make sure to go for lives for safety and a better clear bonus.
• Speedkilling: It's very easy to get overwhelmed by enemy waves. Learning which enemy to go for and which weapon to use is important. Speedkilling bosses is as important too to minimize counter depletion. Especially since a high Gem Counter can reward a large clear bonus.
• Recovery: Triggering the auto-shield is not the end of the world as 1,000 to 5,000 counter value is a mere few large enemies. The most dire situation in Vacant Ark is to lose a life when your counter is close to max value. In most situations you might as well reset. But If you are close to getting an extend drop. Then a 2X Ratio will put you right back on track. High HP enemies such as the shell enemy, the large eel-like enemies with multiple parts in Zone A, the tunnel creepers during Zone B or the shrimp men at zone C are great recovery points. Learning how to deal with those enemies is important to scoring.
• Avoid surplus lives: The bonus that is rewarded when collecting surplus lives is not worth it at all and should be avoided, unless the counter value is maxed out.

Bugs

• End score display: After a run, the displayed score at the top of the screen in the main menu will sometimes display the score before the clear bonus is applied. The actual clear bonus is displayed during the ending. If the player uses the Q button during a session. The score displayed during the ending will show '00'.
• Minor visual bugs/missing sprites: This can happen randomly in some runs. The game was created on an engine meant for Windows 95/98 and most players run it with dgvoodoo. So graphical glitches are bound to happen.

General Tips

• Use the Shallow difficulty as a means to get used to the game's systems.
• In most situations you don't want to use up all of your ammo. Keep 2 to 3 shots for a potential Force use to replenish your ammo.
• Taking down enemies is important for survival, as it inches you closer towards your next extend drop.
• Never use Riot in Abyss difficulty.
• Learn how to Cannon Force. It's a combo in which you use cannon(3 to 4 shots) Switch to Force and use it on a cluster of bullets, rinse and repeat. Incredibly helpful during some bosses in Zone B with high health bullets.
• Understand how to manipulate enemy/boss patterns. Goes without saying, in a general context this is a tip that works well in any shmup. But in Vacant Ark. Lining or hoarding up bullets is a good thing as it can help you recover without switching weapons. e.g. misdirecting the bullets so that they overlap later then using cannon to deal damage to boss but also cancel the overlapping bullets into gems.

Trivia

• Zone A starts with no music and a wave of zakos. The music starts later when the boss appears. Which might be a nod to G-Darius Zone α. The difference is Zone α's music eventually fades in. All zones start with no music but the closest resemblance is Zone A.
• The Track for Zone B-1 and B-2 is called zunchacha~. A homage to Taito's house band Zuntata.
• Buster also made another game called Iwanaga. Taking inspiration from Treasure's Sin and Punishment series.

References

1. The developer's website contains 3 games free to download including Vacant Ark.
2. Vacant Ark's online Manual.
3. Primary info provided by Birb.
4. Files and images provided from the game's files.