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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.

There are fourteen cybernetic upgrades that are available in the shop.

Table 3: Cybernetic Upgrades

Name	Max #	Rarity	Price	Description
Running Speed	8	50%	600	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	8	50%	500	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 melee ability.
Armor	8	50%	600	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	8	50%	600	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	8	50%	400	Mental Protection decreases mental damage taken in combat with 50% for each upgrade. Since ordinary armor does not protect against mental attacks, this upgrade is the only thing that protects you from brain-in-vats and disembodied minds.
Mental Focus	8	50%	500	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	1	50%	500	Map makes the map more detailed and shows items (yellow dots), monsters (pluses) and up and down elevators (arrows) when you access a map terminal.
Ion Stone	2	50%	300	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	1	50%	250	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 has yet died from a little radiation!
Acid Resistance	1	50%	250	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	3	30%	400	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	1	30%	1,200	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	1	30%	750	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	3	30%	500	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.