I don't remember them (never having played planescape except the videogame "Torment" which is awesome by the way)... but I did google them, and found
http://www.mimir.net/monsters/moignorational.shtml and
http://www.mimir.net/monsters/moignoimaginary.shtml which is good enough for me. I think it'd be best to rework them from the ground up though.
First of all, imaginary numbers aren't any more imaginary than rational numbers! It's just that you use positive natural numbers to count discrete things, rationals to compare two things, negatives to describe debt, and "imaginaries" to describe direction. The complex number 0+1i means to rotate 90 degree to the left (off the normal number line). I'd much rather see Imaginary Moignos do plane shift effects than limited wishes.
At any rate... let's see. How many different types can we get? Sorted by my suggested progression of power...
Whole (weakest, it even excludes 0)
Natural (like whole, but with 0)
Rational
Negative (undead?)
Algebraic (necessarily stronger than rational, weaker than complex)
Irrational
Real
Imaginary/Negative Imaginary
Complex
Normal
Uncountable Moigno sets could be divine. Bounded sets would be divine, unbounded cosmic? By which I mean, the Mandelbrot, Cantor sets would be divine, while "Odd Numbers", "Even Numbers", "Prime Numbers" would be cosmic.
That would leave the Alephs alone to be transcendent (aleph-0 is a monad, aleph-1 is a duad, aleph-2 is a triad, etc). Omega would be a demiurge.
Here's some reccomended traits I thought up without any real basis except "2d living mathematical concepts"
Moigno traits
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Moigno are Abberations that embody mathematical concepts, somehow feeding off numbers. All inherent moigno abilities are extraordinary, even when they would seem to be supernatural.
2-Dimensional (Ex): Moigno, being two dimensional creatures, are extremely vulnerable to higher dimensional weapons. As such, moigno suffer an additional x2 damage from critical hits. However, due to the extreme nature of the edge, critical hits delivered from a 2-d creature's natural slam attack automatically possess the sharpness, keen, and vorpal qualities. 2-d weapons deal full damage on a touch attack.
Blindsight (Ex): Moigno don't see like other creatures do, rather they sense the fundamental mathematical nature of existence. They are not subject to gaze attacks, or anything that relies on sight. The distance a particular moigno can sense differs by species.
Sideways Stealing (Ex): As the feat, except as an extraordinary ability. Moigno use this ability to feed.
Unique (Ex): All moigno are considered to be unique beings for the purpose of summon and calling spells.
Moigno possess the Lawful subtype, even if their alignment is chaotic. Chaotic moigno also possess the chaotic subtype. Moigno are never good or evil, nor are they ever true neutral.
Proficient with its natural weapons only.
Proficient with no armor.
Moigno eat, but do not sleep or breathe.