Hollow Ground

MAPS, LEVELS AND DIFFICULTY
The heart of Hollow Ground is the game's dynamic map and level system. It was designed to have a fully scalable map set. The map set can easily be extended by dropping new map files into the game's Maps folder. New maps are constantly added to the game by both the developer and users.

Level Depth Span
The Hollow Ground bunker has 40 levels. The object of the game, as mentioned above, is to find your way down to the lowest level, 2000 feet below the surface, and deal with the biomechanical monstrosity that dwells there.

The standard map set of the game already contains more than 65 maps and is constantly growing by the contribution of many custom maps. Adding a new map does not add a new (depth) level. Maps are instead organized into level depth spans and appear randomly within such a depth span.

The order in which the maps appear is different each time you play the game. This creates a need for both a new approach to managing game difficulty and the player's strategy. Hollow Ground has a very general system for controlling the game difficulty and making sure that progressing deeper down into the bunker always delivers more of a challenge. The simple rule is that most game parameters are multiplied by the level depth span difficulty multiplier (Table 2) for that property. Monsters become tougher on deeper levels and generation rate increases etc. This general approach to managing game difficulty makes the order or the actual depth at which a map appear less relevant. The starter map Ground Floor for instance would be quite a challenge should its level depth span simply be changed to levels 35-39.

Maps usually appear in spans of five levels, but there is nothing preventing a map from being able to appear at any level depth. Many maps overlap one or more of the level depth layers, but it is not recommended to make maps that overlap too many layers or maps that have a level depth span that covers the entire game. The rationale behind layered maps is that game difficulty does not only depend on how tough monsters are. Game difficulty also depends on more structural conditions, that is, the tactical advantage or disadvantage created by the environment. Deeper levels more often have the player at a tactical disadvantage or require him to solve puzzles. Hollow Ground is designed so that game difficulty changes both quantitatively as well as qualitatively as you progress. The above table should give some idea of how the common properties are affected by level depth. The list is not complete. There is another parameter called Fine that affects a lot of subtle things. That and other methods that we use to balance the game are too complex to plot in a table or diagram, but work in much the same way as the Health, Speed and Generation parameters. Also, these parameters are used as variables in functions and algorithms in ways that actually make them more abstract than is conveyed by their names in the table. However, optimizing against the values in the table is a good start.

Notice: You can take any map for a test drive by holding down the ALT key as you select One Player or Two Players from the Main Menu. This enables a dialog box from which you can select any map in the Maps folder. You can also use the left and right arrow keys to select the specific level depth, within the map's level depth span, at which you would like to test the map.

Difficulty Settings
If the default difficulty settings are too easy or too hard for you there is a master difficulty setting in the Preferences Screen that can be set to suit all levels of gamers. This setting does not only make your opponents weaker or stronger, it also changes some other subtle parameters to make the game more suitable to your taste.

Do not be embarrassed if the game is too hard for you even at Moderate Difficulty; Hollow Ground was designed with hardcore gamers in mind. Turn the difficulty down to begin with and hone your skills until you are ready for the tougher settings. Once you get a firm grip of the game's tactical side you will notice that there is a great deal of re-play value. Re-playing does not become repetitive once you understand where the true variation in the game comes from. Do not be fooled by the fact that Hollow Ground has some similarities with first-person action shooters; it is a game of tactics. Hollow Ground will jog both your trigger finger and your brain. Some veteran gamers would tell you that it is so addictive it ought to have a Surgeon General's Warning!

There is also a hidden difficulty mode called Suicide that is activated after you have finished the game once. Suicide difficulty is not impossible, but it is so hard that you need to be a true Hollow Ground master to beat the game at that insane difficulty.

Notice: If you are a very impatient person you might want to cheat by holding down the ALT key while selecting the general difficulty setting in the Preferences Screen to enable Suicide mode without actually having beaten the game. On the other hand if you can't beat the game, you will not survive more than a few seconds in Suicide Mode. This can of course also be handy in case your hi-score file is lost or deleted.

CYBERNETIC UPGRADES
Fitting your different characters with an optimal combination of Cybernetic Upgrades is at the heart of Hollow Ground's strategic side. Each character has his/her individual strengths and weaknesses. Scarse monetary resources as well as a limited number of upgrade slots makes it important to develop a clear upgrade path. Since item availability in the shop is random, each game session is somewhat different, so while a plan is necessary, you always have to be prepared to improvise.

There are mainly two upgrade strategies. One is to primarily enhance the already strong abilities in your characters to create super-mercenaries. The other is to try to make the characters more balanced by evening out the weaknesses. Which strategy works best might depend on your style of gaming and a mix of both might also work well. For more information on optimal upgrade paths you might want to check the Hollow Ground Forum.

^ Table 3: Cybernetic Upgrades ^^^^
 * **Name** | **Max #** | **Rarity** | **Price** |
 * Running Speed | 8 | 50% | 600 |
 * Melee Strength | 8 | 50% | 500 |
 * Armor | 8 | 50% | 600 |
 * Flameproof | 8 | 50% | 600 |
 * Mental Protection | 8 | 50% | 400 |
 * Mental Focus | 8 | 50% | 500 |
 * Map | 1 | 50% | 500 |
 * Ion Stone | 2 | 50% | 300 |
 * Radiation Resistance | 1 | 50% | 250 |
 * Acid Resistance | 1 | 50% | 250 |
 * Regeneration | 3 | 30% | 400 |
 * Marksmanship | 1 | 30% | 1200 |
 * Ammo Clip | 1 | 30% | 750 |
 * Seraph | 3 | 30% | 500 |

The following is a more detailed description of the fourteen cybernetic upgrades that are available in the shop:

RUNNING SPEED increases movement speed with a fixed value of half a square per second for each upgrade. Having one or more speed upgrades is especially important for Walter, who's primary weakness is that he is slow.

MELEE STRENGTH increases damage done in close combat with 50% for each upgrade. It is a common mistake to underestimate close combat as a viable option. Close combat conserves ammo and some mercenaries are actually quite deadly in close combat. The best strategy with this upgrade seems to be to enhance an already powerful meele ability.

ARMOR decreases damage taken in combat with 25% for each upgrade. Remember that damage not taken is damage that you do not need to heal. Armor can be an economically effective alternative to buying lots of separate medical kits.

FLAMEPROOF decreases fire damage taken in combat with 33% for each upgrade. The fire breathing saurants can be quite deadly without this kind of resistance.

MENTAL PROTECTION decreases mental damage taken in combat with 50% for each upgrade. Since ordinary armour does not protect against mental attacks, this upgrade is the only thing that protects you from brain-in-vats and disembodied minds.

MENTAL FOCUS makes psi foci more effective. They last longer, do more damage, heal more etc. For Mortimer, it will also increase the power of his weapons. Give him a couple of these and he will be a veritable killing machine.

MAP makes the map more detailed and shows items (yellow dots), monsters (plus:es) and up and down elevators (arrows) when you access a map terminal.

ION STONE circles around the person and causes a small amount of damage each time it hits an enemy. Each upgrade adds a new ion stone. This is sometimes useful when you are surrounded by enemies. Be careful so that the ion stone does not touch explosive barrels or charges.

RADIATION RESISTANCE will protect you somewhat from the bunker's harmful radiation, causing you to only take a quarter of the damage. However, no one have yet died from a little radiation!

ACID RESISTANCE Lets you walk through acid without getting hurt. Notice that some levels are virtually flooded with acid lakes. Having this resistance permits you to move more freely around such deadly levels.

REGENERATION will make you regenerate your health if it drops below a certain level. More chips installed will make you regenerate faster, and will also raise the health level regeneration kicks in at.

MARKSMANSHIP increases damage done in ranged combat with 50%. Mortimer can not use this upgrade, but take a closer look at the Mental Focus if you need to upgrade his weapons.

AMMO CLIP extends all the character's weapons' ammunition capacity by 50%. Notice that weapon power-ups are decreasing as you use them. It is a good idea to invest in a clip, since it conserves ammo and saves money in the long run.

SERAPH is an autonomous drone that circles around the user and shoots at enemies. You will find its extra fire power very useful regardless of which character you are playing. Notice: only found in version 1.0.2 and later.

PSI FOCI CANISTERS
Psi-foci can be used by all of the mercenaries, but the duration, area of effect and power of a psi-focus depends on the user's mental power ability. Mortimer has the highest initial mental power. Developing his mental power by fitting Mental Power Upgrades makes him a veritable psionic killing machine.

The Psi-Focus Canisters differ from the Cybernetic Upgrades in some ways. Canisters can be found throughout the levels (as well as in the shop). Canisters are consumed when used. You can only carry one canister at a time. Psi-Focus effects have shorter duration, but can be very powerful. ^ Table 4: Psi Foci Canisters ^^^ The following is a more detailed description of the twelve psi-focus canisters that are available in the game:
 * **Name** | **Rarity** | **Price** |
 * Regenerate | 50% | 200 |
 * Fatal Blast | 60% | 200 |
 * Invisibility | 50% | 200 |
 * Instant Recall | 50% | 150 |
 * Instant Exit | 10% | 500 |
 * Paralysis | 50% | 200 |
 * Time Stop | 50% | 150 |
 * Confusion | 50% | 200 |
 * Fear | 50% | 200 |
 * Telekinesis | 50% | 150 |
 * Lightning Strike | 60% | 200 |
 * Fire Shield | 60% | 250 |

REGENERATE increases the health of all active mercenaries with 150 points as well as an additional 150 points per the user's mental power level for the duration of the focus. Since the effect is affected by the user's mental power level, this is a powerful healing ability in the hands of a skilled psionicist.

FATAL BLAST creates a psionic explosion originating from the user and having a blast area proportional to his mental power. The amount of damage done is also determined by the user's mental power. Remember that machines only take one-quarter damage from mental attacks. Brains-in-vats and Disembodied Minds on the other hand are more vulnerable to this kind of damage.

INVISIBILITY makes the user invisible to enemies. They will stop hunting the invisible person, but can still do damage to him. The invisibility psi-focus is thus not very useful in two-player mode when the mercenaries are lined up in a narrow corridor, unless both of them are invisible. Monsters will not fight back if an invisible person attacks them from a distance, so it is very useful in large open rooms. The duration of invisibility is determined by the user's mental power.

INSTANT RECALL teleports the user (and his companion) directly back to the level's entrance. This is sometimes the only method to exit a level where you accidentally get stuck. You can also use it to get out of a tight spot when surrounded by enemies.

INSTANT EXIT teleports the user (and his companion) directly to the level's active exit elevator. This is sometimes the only method to exit a level where you accidentally get stuck, or even to get past a particularly nasty level.

PARALYSIS makes enemies unable to move for the duration of the focus. Non-living enemies like robots or gun turrets only have a 50% chance of being affected. The duration of the paralysis is determined by the user's mental power.

TIME STOP halts the timer that is activated on some levels either as the player characters enter or because they activated it by shooting a blow-up switch. The timer is halted for the duration of the focus, which is determined by the user's mental power.

CONFUSION makes enemies confused. They act irrationally and no longer move with a purpose (which is often to hunt the mercenaries). Non-living enemies like robots or gun turrets only have a 50% chance of being confused. Notice: there is a bug in version 1.0.1 that makes this psi-foci canister unusable; we have fixed it in version 1.0.2.

FEAR makes enemies scared of the user and will do everything they can to avoid him or her. It is, however, only the user that frightens them, and it is therefore a good idea for him or her to walk first, to scare the enemies away. The duration of the fear is determined by the user's mental power.

TELEKINESIS makes all small items fly towards the user. The user can collect items without having to get close to them and can sometimes get items that are otherwise hard or very dangerous to reach. Barrels are not small enough to be affected by the telekinesis and the same goes for all creatures regardless of size. The duration of the telekinesis, as well as the range items are attracted from is determined by the user's mental power.

LIGHTNING STRIKE creates a rain of lightning bolts that shoots from the user in all directions. The lightning bolts make electrical damage, which is especially useful against robots and other kinds of machines. The amount of damage done depends on the user's mental power.

FIRE SHIELD creates a cloud of fire around the user. The amount of fire damage done, the duration, and how far the flames reach out depend on the user's mental power. This is a formidable weapon, especially in the hands of a powered-up Mortimer. The fire shield can be your only hope on some levels that are veritable hatcheries of deadly enemies. Have both Mortimer and the other character buy one and then use the trade trick to transfer the second fire shield to Mortimer once he has used his own canister.

MONSTERS
Without the horde of mutated freaks that haunt the bunker, Hollow Ground would just be about navigating the labyrinthine tunnels to find the exit. Enter monsters. This bloodthirsty gang will do their best to blast any ill-prepared mercenaries to bits.

Monster stats and difficulty
The monster stats are not static. Monsters get tougher as is described in Table 2 (section on Maps, Levels and Difficulty). It works something like this. Each level span has a difficulty multiplier. You can also set the general difficulty level in the Preferences Screen (which is also a multiplier). These two multipliers represent the current difficulty at any given time. Individual stats are expressed as base values. The monsters actual stat is the result of multiplying the current difficulty multiplier with the base value. In the below table I have listed the stat base values. Actual stat values are filled out when the monster is generated. ^ Table 5: Monster base stats ^^^^^
 * Name | Health | Speed | Range | Score |
 * Amoeba | 3 000 | 1.0 | -- | 200 |
 * Battle Droid | 5 000 | 0.75 | 36 | 3 500 |
 * Brain-in-a-vat * | 4 000 | 0.25 | -- | 1 000 |
 * Disembodied Mind | 125 | 2.5 | 80 | 150 |
 * Drone | 320 | 0.80 | 24 | 100 |
 * Chaos Marine, laser | 100 | 1.25 | 24 | 50 |
 * Chaos Marine, mortar | 100 | 1.20 | 16 | 50 |
 * Cyborg Zombie | 50 | 0.75 | -- | 10 |
 * Grunt | 150 | 1.25 | -- | 50 |
 * Saurant, fire | 200 | 2 | 16 | 200 |
 * Saurant, poison | 200 | 2 | 12 | 200 |
 * Saurant, electric | 200 | 2 | 32 | 250 |
 * Spider, giant | 350 | 1.0 | 20 | 150 |
 * Spider, small | 50 | 1.75 | -- | 150 |
 * Squatter | 90 | 2.20 | -- | -- |
 * Turret | 1 200 | 10 | 32 | 350 |
 * End-boss, head | 10 000 | 10 | 32 | 25 000 |
 * End-boss, body | 25 000 | -- | -- | 100 000 |
 * Brains-in-a-vat's health is calculated as 4 000 + (1 000 x difficulty) and their speed is calculated as 0.25 + (1.0 x difficulty).|||||

Notice: Additionally, monsters also have a property called randomness. This value is used to control the amount of randomness in monster behavior and properties, so base values are always ballpark figures.

Until someone sits down and writes a proper guide on characters it might be interesting to know that Walter (the marine) makes 10 points of damage per shot with his rifle. This base damage is multiplied with his weapon power-up level. Things are however not as simple as this might imply, at least with the game's missile weapons. First, weapon power-up effectiveness does not increase with one for each power-up. Second, missiles make damage each time they collide with the monster and all missiles collide a number of times before they are destroyed. The best example is Walter's laser, which makes 8 + (2 x power level) points of damage each collision as it passes through a monster. This is the reason why most weapons are more powerful than the base damage seems to imply. Walter does not need to shoot a Grunt 15 times with his rifle at power-up level one to kill it! The exact number of times depend on so many factors that it is best to leave it for another part of the guide.

Monster damage resistances
The monster stats are, of course, of no real use unless you also have stats for the player characters' weapon damage, armor etc. You can, however, estimate using the base values, the level span multipliers and counting the number of shots that is required to kill a monster at a particular level. On the other hand, monsters have something called resistances, which is another way of saying they are more or less immune to some form of attacks. You need to select the right weapon for a particular monster or your weapon power-ups just won't do you much good. I have listed each monster's resistances and weakness to the five different types of damage in the below table.

^ Table 6: Monster resistances and weaknesses^^^^^^
 * Name | Fire | Mental | Electric | Acid | Normal |
 * Battle Droid | 50% | 75% | x2 | -- | -- |
 * Drone | 50% | 75% | x2 | -- | -- |
 * Turret | 50% | 75% | x2 | -- | -- |
 * Brain-in-a-vat | -- | x4 | -- | -- | -- |
 * Disembodied Mind | -- | x4 | -- | -- | -- |