Psionics

The number you roll when determining the amount of a character’s psionic power is their psionic strength. A character has attack strength and defense strength which are both equal to psionic strength. Another statistic, psionic ability, is equal to double psionic strength.1) PHB 110.

Attack and defense modes

Using psionic attack modes costs attack strength, while using psionic defense modes costs defense strength. Running out of either points means you can’t use attack modes or defense modes, respectively. Being unable to defend means you can be attacked on the special table that has all the bad stuff on it (brain getting fried, and so on).2) PHB 110-111.

Lost modes might be regained through a wish.

Disciplines

Using psionic disciplines (devotions and sciences) costs psionic strength, which means that for each point spent on a discipline, the user loses one point of attack strength and one point of defense strength.3) PHB 111.

Level of mastery for disciplines is equal to the character’s highest class level.4) Some people play with the level of mastery counting from the class level at which the discipline was obtained, but the core books seem pretty clear that this is wrong. Also, imagine DMing for a bunch of psionic NPCs who all got their powers at different levels. Exceptions: Some disciplines list alternate determinations for level of mastery with regard to that discipline.

Psions roll for disciplines as they acquire them. Only the first one is rolled for at character creation.

Clairaudience and clairvoyance

Clairaudience and clairvoyance have the unlimited range of the spell versions and have the additional ability to be targeted in unknown areas within the range listed for the psionic ability.

Invisibility

Dragon mag 78 sage advice:

Q: Does the “Detection of Invisibility” table on p. 60 of the DMG apply to psionic invisibility? Can a character using the discipline of invisibility attack another creature and still remain invisible to that creature? A: No on both counts. First, psionic invisibility involves mind control, not “light waves or similar physical manifestations”. (Players Handbook, p. 113), and hence cannot be detected by intelligent creatures the same way they might be able to sense someone who was rendered invisible by magical means. Someone employing the mind bar discipline is not subject to this mind control, however, and thus is able to “see through” the deception. Second, a character using psionic invisibility cannot attack at the same time because he must concentrate on the application of the discipline to maintain his invisible state. Unless otherwise specified in a particular description, no psionic attack mode or discipline can be employed while the user's mind is distracted or engaged in some other decision-making activity.