There is no "Z" psionic monster, so to end this month-long consideration of psionic monsters, I want to go over the guidelines/rules of psionic combat, which will be necessary if you begin to incorporate these wonderful psi-monsters into your adventures.
The Benevolent Utility of Rounds rather than Segments
Famously, psionic powers take only seconds to launch, measured in attacks per segment, rather than full rounds. I strongly recommend you "house-rule" a modification on this, as that one rule causes most of the practical problems when integrating psionics into normal combat.
The biggest problems with psionic combat in segments are that
1) psionic combat, taking place before regular combat, means that your psionic PC could be knocked out dead before any real action happens, without any help possible from the rest of the party, and
2) sitting around the table, it is unfair and boring to the non-psionic players to watch the unfolding of psionic combat to the exclusion of everyone else.
Thus, I strongly recommend you "house rule" psionic combat to take place in normal rounds, along with everything else. It makes psionic easily and smoothly incorporated into the normal combat sequence.
It makes perfect sense to have one psionic attack per round. Otherwise, are we to allow the Mind Flayer to fire off 10 Psionic Blasts per round? That would not make any sense and is obviously not what the designers intended.
Psionics Attacks Handled as All Other Attacks
Logically, a psionic attack should be handled just like a magical or physical attack: 1 type of attack, 1 attack per round. In other words, in your round, you get one attack: physical, magical, or psionic.
Handling psionic combat in this manner allows psionics to be smoothly integrated into the normal flow of the game. Psionic players are no longer getting knocked out before combat starts, nor is everyone else sitting around bored. Plus, it makes sense according to the in-game mechanics.
Handling Psionics Considering Initiative
Psionics would then be subject to the same rules of initiative as everything else, as well. Let's say a monster WINS INITIATIVE and directs a psionic attack at your PC group.
--Those WITH psionic defences put up the defence of their choice, and subtract some points from their psionic total. They then get their attack.
--Those WITHOUT psionic defenses have to make a savings throw against the psionic attack.
If they succeed on their save, they "throw off" the psionic attack and get to counter-attack like normal.
If they fail their save, they suffer the ill effects as specified in the appropriate table, and probably lose their counter-attack, due to the result of the effect.
A spell caster who failed his savings throw would have his spell interrupted and ruined for that round. Passing his save, he could cast the spell as normal.
If the PCs won the initiative that round, they would get their attacks off first, magical, psionic, or physical, before suffering the psionic attack.
Dispense with table IV.B. (the Table of Certain Psionic Doom)
This table is the "Psionic Attack Upon Defenseless Psionic" table (on page 77 of the 1e DMG). The devastating effects of this table are the second leading cause of people dumping psionics from their campaigns.
Playing a psionic PC becomes very un-fun when you get down to this table, and if you meet a monster with a higher psionic point total, under the "attacks-in-segments" routine, you are pretty much guaranteed to get down to this table.
If you change psionic combat to "attacks per round", you are a lot less likely to get down to this table. But there are still some logical reasons to just get rid of it altogether.
As an alternative, if your psionic PC runs out of psionic strength points, just have him make a savings throw as a non-psionic. Really bad stuff is still possible, but it becomes far less likely.
See my savings throw tables for non-psionics versus the various psionic attacks:
Should You Divide Attack and Defense Points?
I think this is another rule that should tossed for the sake of simplicity [but you could still keep it if you did not mind the extra "accounting load" and illogic of it all].
Supposedly, if you run out of defense points, you could still attack with psionics, and could still use your psionic powers, but you would be considered "defenseless"? Frankly, it doesn't make sense. If you have psi strength left, you should be able to use it. Separating them also adds to the "complication load" due to the extra accounting and necessity of "half points". Screw it.
Instead, just keep one running tally: total strength/ability points. In other words, psionic strength is the same thing as psionic ability. That total can be used for attack, defense, or disciplines/sciences, until the points run out. Only then you are truly a "defenseless psionic". [Following this "easy button" rule also eliminates the problem of subtracting "half-points" when using disciplines/sciences.]
Conclusion
If you incorporate these three simple house rules into your game -- attacks in rounds, no table IV.B., and no division of strength points - psionics become a pleasurable and easily-administered element in your regular campaign. Enjoy!
