Psionic Disciplines

In System Shock 2, Psionic Disciplines or Psi Powers, are abilities that soldier uses to cause a variety of effects in the game. Some Disciplines are offensive, some defensive, some affect the player's statistic or skill values, some result in status effects, and others provide some other special ability. Psionic Disciplines require the player to wield a Psi Amp to use, depend on Psionic Ability statistic (or PSI) and consume Psi Points when activated.

Since Psionics fills the same role that magic does in a fantasy RPG, Psionic Disciplines correspond to individual spells. Carrying this analogy through shows that the Psi Amp fills the role of a wand, Psi Points like magic points or spell points, and Psi Tiers like spell levels.

New Psionic Disciplines are unlocked at Psi Upgrade Units using Cybernetic Modules.

Tiers
Psionic Disciplines are grouped into five Tiers, or levels. The number of the Tier equals the number of Psi Points required to activate any particular Discipline from that Tier. That is, Tier Four Disciplines require four Psi Points to use. Each Tier contains seven Disciplines, giving a total of 35 available Disciplines in the game.

Prior to acquiring any new Psionic Discipline, the player must have also unlocked the Tier to which that Psionic Discipline belongs. This is also done at Psi Upgrade Units, and costs the same number of Cybernetic Modules as a Discipline for that Tier. Tier unlock upgrades are not Disciplines, and have two passive effects: They make it possible to unlock Psionic Disciplines at that Tier, and they provide a permanent increase in Psi Points equal to twice the level number. Thus, unlocking Tier Five increases maximum Psi Points by ten (2 × 5). Tiers need not be unlocked in order, or at all.

After training, all OSA Agents start with Tier One and Tier Two unlocked, along with the Projected Cryokinesis Discipline and any two of the other six Tier One Disciplines.

Overloading
Some Psi Disciplines can be overloaded to increase their effectiveness, by holding down the left mouse button. A progress bar will appear in the center of the screen, filling as you continue to hold the mouse button. Once it reaches the yellow box at the right side of the bar, release the button and the Psi Power will be cast with a bonus of +2 to your PSI stat, to a maximum effective PSI of 10 (however, for that the player needs to have PSI 8 before casting).



Missing the yellow box by releasing too early uses the Psi Power at its normal level. Releasing too late causes Psi Burnout. The Power will fail, and you take damage unless you've installed the Power Psi O/S Upgrade or you have high enough PSI (only 8 is wholly safe though). The progress bar moves faster for higher Tier Psi Disciplines, increasing the difficulty of overloading. It is worth noting that upgrading the PSI stat also makes the yellow overload box bigger, easing overloading.

Cybernetic Module costs
The cost of any Psi Upgrade Unit item depends on the Tier and difficulty level. The cost of any given Tier is the floor of one-and-two-thirds times the cost of the next Tier down. That is, a Tier Two upgrade costs one-and-two-thirds times what a Tier One upgrade costs, rounded down. Tier Three the same with respect to Tier Two, and so on. These values are then scaled according to the difficulty level.

While there are technically enough Cybernetic Modules in the game to obtain all 35 Psionic Disciplines, the cost on Hard and Impossible would be over half of them. As a result, few players opt to get every Psionic Discipline.

Offensive Disciplines
These are the Disciplines that cause damage to others.

Defensive Disciplines
These reduce damage from a variety of sources.

Healing Disciplines
These Disciplines directly refill the player's Hit Point pool.

Self-targeted
These Disciplines affect player stats that are used in a variety of calculations. In most RPGs these would be called "buffs".

Non-self targeted
These Disciplines cause status effects to others. In many RPGs these would be called "debuffs".

Other Disciplines
These Disciplines cause a variety of effects.